ah-stl-functional_test.cc

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/*
                          Aleph_w
 
  Data structures & Algorithms
  version 2.0.0b
  https://github.com/lrleon/Aleph-w
 
  This file is part of Aleph-w library
 
  Copyright (c) 2002-2026 Leandro Rabindranath Leon
 
  Permission is hereby granted, free of charge, to any person obtaining a copy
  of this software and associated documentation files (the "Software"), to deal
  in the Software without restriction, including without limitation the rights
  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  copies of the Software, and to permit persons to whom the Software is
  furnished to do so, subject to the following conditions:
 
  The above copyright notice and this permission notice shall be included in all
  copies or substantial portions of the Software.
 
  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  SOFTWARE.
*/
 
 
#include <gtest/gtest.h>
#include <numeric>
#include <ah-stl-functional.H>
 
#include <vector>
#include <list>
#include <deque>
#include <string>
 
using namespace Aleph;
 
//==============================================================================
// Range Generation Tests
//==============================================================================
 
TEST(StlRange, BasicRange)
{
  auto r = stl_range(1, 5);
  EXPECT_EQ(r.size(), 5);
  EXPECT_EQ(r[0], 1);
  EXPECT_EQ(r[4], 5);
}
 
TEST(StlRange, RangeWithStep)
{
  auto r = stl_range(0, 10, 2);
  EXPECT_EQ(r.size(), 6);
  EXPECT_EQ(r[0], 0);
  EXPECT_EQ(r[5], 10);
}
 
TEST(StlRange, SingleArgRange)
{
  auto r = stl_range(5);
  EXPECT_EQ(r.size(), 5);
  EXPECT_EQ(r[0], 0);
  EXPECT_EQ(r[4], 4);
}
 
TEST(StlLinspace, Basic)
{
  auto r = stl_linspace(0.0, 1.0, 5);
  EXPECT_EQ(r.size(), 5);
  EXPECT_DOUBLE_EQ(r[0], 0.0);
  EXPECT_DOUBLE_EQ(r[4], 1.0);
}
 
TEST(StlRep, Basic)
{
  auto r = stl_rep(5, 42);
  EXPECT_EQ(r.size(), 5);
  for (int x : r)
    EXPECT_EQ(x, 42);
}
 
TEST(StlGenerate, Basic)
{
  auto r = stl_generate(5, [](size_t i) { return i * i; });
  EXPECT_EQ(r.size(), 5);
  EXPECT_EQ(r[0], 0);
  EXPECT_EQ(r[2], 4);
  EXPECT_EQ(r[4], 16);
}
 
//==============================================================================
// Core Functional Operations Tests
//==============================================================================
 
TEST(StlForEach, Basic)
{
  std::vector<int> v = {1, 2, 3, 4, 5};
  int sum = 0;
  stl_for_each([&sum](int x) { sum += x; }, v);
  EXPECT_EQ(sum, 15);
}
 
TEST(StlForEachIndexed, Basic)
{
  std::vector<std::string> v = {"a", "b", "c"};
  std::vector<std::string> results;
  stl_for_each_indexed([&results](size_t i, const std::string& s) {
    results.push_back(std::to_string(i) + ":" + s);
  }, v);
  
  EXPECT_EQ(results[0], "0:a");
  EXPECT_EQ(results[2], "2:c");
}
 
TEST(StlMap, Basic)
{
  std::vector<int> v = {1, 2, 3, 4, 5};
  auto squares = stl_map([](int x) { return x * x; }, v);
  
  EXPECT_EQ(squares.size(), 5);
  EXPECT_EQ(squares[0], 1);
  EXPECT_EQ(squares[2], 9);
  EXPECT_EQ(squares[4], 25);
}
 
TEST(StlMap, TypeChange)
{
  std::vector<int> v = {1, 2, 3};
  auto strings = stl_map([](int x) { return std::to_string(x); }, v);
  
  EXPECT_EQ(strings[0], "1");
  EXPECT_EQ(strings[2], "3");
}
 
TEST(StlMapi, Basic)
{
  std::vector<std::string> v = {"a", "b", "c"};
  auto results = stl_mapi([](size_t i, const std::string& s) {
    return std::to_string(i) + s;
  }, v);
  
  EXPECT_EQ(results[0], "0a");
  EXPECT_EQ(results[2], "2c");
}
 
TEST(StlFilter, Basic)
{
  std::vector<int> v = {1, 2, 3, 4, 5, 6};
  auto evens = stl_filter([](int x) { return x % 2 == 0; }, v);
  
  EXPECT_EQ(evens.size(), 3);
  EXPECT_EQ(evens[0], 2);
  EXPECT_EQ(evens[2], 6);
}
 
TEST(StlFilteri, EvenIndices)
{
  std::vector<int> v = {10, 20, 30, 40, 50};
  auto evens = stl_filteri([](size_t i, int) { return i % 2 == 0; }, v);
  
  EXPECT_EQ(evens.size(), 3);
  EXPECT_EQ(evens[0], 10);
  EXPECT_EQ(evens[1], 30);
  EXPECT_EQ(evens[2], 50);
}
 
//==============================================================================
// Fold Tests
//==============================================================================
 
TEST(StlFoldl, Sum)
{
  std::vector<int> v = {1, 2, 3, 4, 5};
  int sum = stl_foldl(0, [](int acc, int x) { return acc + x; }, v);
  EXPECT_EQ(sum, 15);
}
 
TEST(StlFoldl, Product)
{
  std::vector<int> v = {1, 2, 3, 4};
  int product = stl_foldl(1, [](int acc, int x) { return acc * x; }, v);
  EXPECT_EQ(product, 24);
}
 
TEST(StlFoldr, Subtraction)
{
  // Right fold: 1 - (2 - (3 - 0)) = 1 - (2 - 3) = 1 - (-1) = 2
  std::vector<int> v = {1, 2, 3};
  int result = stl_foldr(0, [](int x, int acc) { return x - acc; }, v);
  EXPECT_EQ(result, 2);
}
 
TEST(StlFoldr, ListConstruction)
{
  // Right fold to construct string: "1" + ("2" + ("3" + ""))
  std::vector<int> v = {1, 2, 3};
  std::string result = stl_foldr(std::string(""), [](int x, std::string acc) {
    return std::to_string(x) + acc;
  }, v);
  EXPECT_EQ(result, "123");
}
 
TEST(StlScanLeft, RunningSum)
{
  std::vector<int> v = {1, 2, 3, 4};
  auto sums = stl_scan_left(0, [](int acc, int x) { return acc + x; }, v);
  
  EXPECT_EQ(sums.size(), 5);
  EXPECT_EQ(sums[0], 0);   // init
  EXPECT_EQ(sums[1], 1);   // 0 + 1
  EXPECT_EQ(sums[2], 3);   // 1 + 2
  EXPECT_EQ(sums[3], 6);   // 3 + 3
  EXPECT_EQ(sums[4], 10);  // 6 + 4
}
 
TEST(StlScanRight, Basic)
{
  std::vector<int> v = {1, 2, 3};
  auto results = stl_scan_right(0, [](int x, int acc) { return x + acc; }, v);
  
  // scan_right [1,2,3] with + and 0: [6, 5, 3, 0]
  EXPECT_EQ(results.size(), 4);
  EXPECT_EQ(results[0], 6);  // 1+2+3+0
  EXPECT_EQ(results[1], 5);  // 2+3+0
  EXPECT_EQ(results[2], 3);  // 3+0
  EXPECT_EQ(results[3], 0);  // init
}
 
//==============================================================================
// Predicate Tests
//==============================================================================
 
TEST(StlAll, AllTrue)
{
  std::vector<int> v = {2, 4, 6, 8};
  EXPECT_TRUE(stl_all([](int x) { return x % 2 == 0; }, v));
}
 
TEST(StlAll, SomeFalse)
{
  std::vector<int> v = {2, 3, 6, 8};
  EXPECT_FALSE(stl_all([](int x) { return x % 2 == 0; }, v));
}
 
TEST(StlExists, SomeTrue)
{
  std::vector<int> v = {1, 2, 3, 4, 5};
  EXPECT_TRUE(stl_exists([](int x) { return x == 3; }, v));
}
 
TEST(StlExists, NoneTrue)
{
  std::vector<int> v = {1, 2, 3, 4, 5};
  EXPECT_FALSE(stl_exists([](int x) { return x == 10; }, v));
}
 
TEST(StlNone, Basic)
{
  std::vector<int> v = {1, 3, 5, 7};
  EXPECT_TRUE(stl_none([](int x) { return x % 2 == 0; }, v));
}
 
//==============================================================================
// Finding Tests
//==============================================================================
 
TEST(StlFind, Found)
{
  std::vector<int> v = {1, 2, 3, 4, 5};
  auto result = stl_find([](int x) { return x > 3; }, v);
  
  ASSERT_TRUE(result.has_value());
  EXPECT_EQ(*result, 4);
}
 
TEST(StlFind, NotFound)
{
  std::vector<int> v = {1, 2, 3};
  auto result = stl_find([](int x) { return x > 10; }, v);
  
  EXPECT_FALSE(result.has_value());
}
 
TEST(StlFindLast, Found)
{
  std::vector<int> v = {1, 2, 3, 4, 5};
  auto result = stl_find_last([](int x) { return x % 2 == 0; }, v);
  
  ASSERT_TRUE(result.has_value());
  EXPECT_EQ(*result, 4);
}
 
TEST(StlFindIndex, Found)
{
  std::vector<std::string> v = {"a", "b", "c", "d"};
  auto result = stl_find_index([](const std::string& s) { return s == "c"; }, v);
  
  ASSERT_TRUE(result.has_value());
  EXPECT_EQ(*result, 2);
}
 
TEST(StlFindMapi, Found)
{
  std::vector<int> v = {1, 2, 3, 4, 5};
  auto result = stl_find_mapi([](size_t i, int x) -> std::optional<std::string> {
    if (x == 3)
      return "found at " + std::to_string(i);
    return std::nullopt;
  }, v);
  
  ASSERT_TRUE(result.has_value());
  EXPECT_EQ(*result, "found at 2");
}
 
TEST(StlMem, Found)
{
  std::vector<int> v = {1, 2, 3, 4, 5};
  EXPECT_TRUE(stl_mem(3, v));
  EXPECT_FALSE(stl_mem(10, v));
}
 
//==============================================================================
// Counting Tests
//==============================================================================
 
TEST(StlCount, Basic)
{
  std::vector<int> v = {1, 2, 3, 4, 5, 6};
  size_t count = stl_count([](int x) { return x % 2 == 0; }, v);
  EXPECT_EQ(count, 3);
}
 
TEST(StlCountValue, Basic)
{
  std::vector<int> v = {1, 2, 2, 3, 2, 4};
  EXPECT_EQ(stl_count_value(2, v), 3);
}
 
//==============================================================================
// Take and Drop Tests
//==============================================================================
 
TEST(StlTake, Basic)
{
  std::vector<int> v = {1, 2, 3, 4, 5};
  auto result = stl_take(3, v);
  
  EXPECT_EQ(result.size(), 3);
  EXPECT_EQ(result[0], 1);
  EXPECT_EQ(result[2], 3);
}
 
TEST(StlDrop, Basic)
{
  std::vector<int> v = {1, 2, 3, 4, 5};
  auto result = stl_drop(2, v);
  
  EXPECT_EQ(result.size(), 3);
  EXPECT_EQ(result[0], 3);
  EXPECT_EQ(result[2], 5);
}
 
TEST(StlTakeLast, Basic)
{
  std::vector<int> v = {1, 2, 3, 4, 5};
  auto result = stl_take_last(3, v);
  
  EXPECT_EQ(result.size(), 3);
  EXPECT_EQ(result[0], 3);
  EXPECT_EQ(result[2], 5);
}
 
TEST(StlTakeWhile, Basic)
{
  std::vector<int> v = {1, 2, 3, 10, 4, 5};
  auto result = stl_take_while([](int x) { return x < 10; }, v);
  
  EXPECT_EQ(result.size(), 3);
  EXPECT_EQ(result[2], 3);
}
 
TEST(StlDropWhile, Basic)
{
  std::vector<int> v = {1, 2, 3, 10, 4, 5};
  auto result = stl_drop_while([](int x) { return x < 10; }, v);
  
  EXPECT_EQ(result.size(), 3);
  EXPECT_EQ(result[0], 10);
}
 
//==============================================================================
// Accessing Tests
//==============================================================================
 
TEST(StlFirst, Basic)
{
  std::vector<int> v = {10, 20, 30};
  auto result = stl_first(v);
  
  ASSERT_TRUE(result.has_value());
  EXPECT_EQ(*result, 10);
}
 
TEST(StlFirst, Empty)
{
  std::vector<int> v;
  auto result = stl_first(v);
  
  EXPECT_FALSE(result.has_value());
}
 
TEST(StlLast, Basic)
{
  std::vector<int> v = {10, 20, 30};
  auto result = stl_last(v);
  
  ASSERT_TRUE(result.has_value());
  EXPECT_EQ(*result, 30);
}
 
TEST(StlNth, Basic)
{
  std::vector<int> v = {10, 20, 30, 40, 50};
  auto result = stl_nth(2, v);
  
  ASSERT_TRUE(result.has_value());
  EXPECT_EQ(*result, 30);
}
 
//==============================================================================
// Min/Max Tests
//==============================================================================
 
TEST(StlMin, Basic)
{
  std::vector<int> v = {3, 1, 4, 1, 5, 9};
  auto result = stl_min(v);
  
  ASSERT_TRUE(result.has_value());
  EXPECT_EQ(*result, 1);
}
 
TEST(StlMax, Basic)
{
  std::vector<int> v = {3, 1, 4, 1, 5, 9};
  auto result = stl_max(v);
  
  ASSERT_TRUE(result.has_value());
  EXPECT_EQ(*result, 9);
}
 
TEST(StlMinMax, Basic)
{
  std::vector<int> v = {3, 1, 4, 1, 5, 9};
  auto result = stl_min_max(v);
  
  ASSERT_TRUE(result.has_value());
  EXPECT_EQ(result->first, 1);
  EXPECT_EQ(result->second, 9);
}
 
TEST(StlMinBy, Basic)
{
  std::vector<std::string> v = {"hello", "a", "world"};
  auto result = stl_min_by([](const std::string& s) { return s.length(); }, v);
  
  ASSERT_TRUE(result.has_value());
  EXPECT_EQ(*result, "a");
}
 
TEST(StlMaxBy, Basic)
{
  std::vector<std::string> v = {"hello", "a", "world"};
  auto result = stl_max_by([](const std::string& s) { return s.length(); }, v);
  
  ASSERT_TRUE(result.has_value());
  EXPECT_EQ(*result, "hello");
}
 
//==============================================================================
// Sum and Product Tests
//==============================================================================
 
TEST(StlSum, Basic)
{
  std::vector<int> v = {1, 2, 3, 4, 5};
  EXPECT_EQ(stl_sum(v), 15);
}
 
TEST(StlProduct, Basic)
{
  std::vector<int> v = {1, 2, 3, 4};
  EXPECT_EQ(stl_product(v), 24);
}
 
//==============================================================================
// Partition Tests
//==============================================================================
 
TEST(StlPartition, Basic)
{
  std::vector<int> v = {1, 2, 3, 4, 5, 6};
  auto [evens, odds] = stl_partition([](int x) { return x % 2 == 0; }, v);
  
  EXPECT_EQ(evens.size(), 3);
  EXPECT_EQ(odds.size(), 3);
}
 
//==============================================================================
// Zip and Enumerate Tests
//==============================================================================
 
TEST(StlZipToPairs, Basic)
{
  std::vector<int> v1 = {1, 2, 3};
  std::vector<std::string> v2 = {"a", "b", "c"};
  
  auto result = stl_zip_to_pairs(v1, v2);
  
  EXPECT_EQ(result.size(), 3);
  EXPECT_EQ(result[0].first, 1);
  EXPECT_EQ(result[0].second, "a");
}
 
TEST(StlUnzipPairs, Basic)
{
  std::vector<std::pair<int, std::string>> v = {{1, "a"}, {2, "b"}, {3, "c"}};
  
  auto [nums, strs] = stl_unzip_pairs(v);
  
  EXPECT_EQ(nums.size(), 3);
  EXPECT_EQ(strs.size(), 3);
  EXPECT_EQ(nums[1], 2);
  EXPECT_EQ(strs[1], "b");
}
 
TEST(StlEnumerateToPairs, Basic)
{
  std::vector<std::string> v = {"a", "b", "c"};
  
  auto result = stl_enumerate_to_pairs(v);
  
  EXPECT_EQ(result.size(), 3);
  EXPECT_EQ(result[0].first, 0);
  EXPECT_EQ(result[0].second, "a");
  EXPECT_EQ(result[2].first, 2);
}
 
//==============================================================================
// Comparison Tests
//==============================================================================
 
TEST(StlEqual, Equal)
{
  std::vector<int> v1 = {1, 2, 3};
  std::vector<int> v2 = {1, 2, 3};
  
  EXPECT_TRUE(stl_equal(v1, v2));
}
 
TEST(StlEqual, NotEqual)
{
  std::vector<int> v1 = {1, 2, 3};
  std::vector<int> v2 = {1, 2, 4};
  
  EXPECT_FALSE(stl_equal(v1, v2));
}
 
TEST(StlCompare, Equal)
{
  std::vector<int> v1 = {1, 2, 3};
  std::vector<int> v2 = {1, 2, 3};
  
  EXPECT_EQ(stl_compare(v1, v2), 0);
}
 
TEST(StlCompare, Less)
{
  std::vector<int> v1 = {1, 2, 3};
  std::vector<int> v2 = {1, 2, 4};
  
  EXPECT_EQ(stl_compare(v1, v2), -1);
}
 
TEST(StlCompare, Greater)
{
  std::vector<int> v1 = {1, 2, 4};
  std::vector<int> v2 = {1, 2, 3};
  
  EXPECT_EQ(stl_compare(v1, v2), 1);
}
 
//==============================================================================
// Reverse and Sort Tests
//==============================================================================
 
TEST(StlReverse, Basic)
{
  std::vector<int> v = {1, 2, 3, 4, 5};
  auto result = stl_reverse(v);
  
  EXPECT_EQ(result[0], 5);
  EXPECT_EQ(result[4], 1);
}
 
TEST(StlSort, Basic)
{
  std::vector<int> v = {3, 1, 4, 1, 5, 9};
  auto result = stl_sort(v);
  
  EXPECT_EQ(result[0], 1);
  EXPECT_EQ(result[5], 9);
}
 
TEST(StlSortBy, Basic)
{
  std::vector<std::string> v = {"hello", "a", "world"};
  auto result = stl_sort_by([](const std::string& a, const std::string& b) {
    return a.length() < b.length();
  }, v);
  
  EXPECT_EQ(result[0], "a");
  EXPECT_EQ(result[2], "world");
}
 
//==============================================================================
// Uniqueness Tests
//==============================================================================
 
TEST(StlUnique, Basic)
{
  std::vector<int> v = {1, 1, 2, 2, 2, 3, 3};
  auto result = stl_unique(v);
  
  EXPECT_EQ(result.size(), 3);
  EXPECT_EQ(result[0], 1);
  EXPECT_EQ(result[1], 2);
  EXPECT_EQ(result[2], 3);
}
 
TEST(StlDistinct, Basic)
{
  std::vector<int> v = {1, 2, 1, 3, 2, 4};
  auto result = stl_distinct(v);
  
  EXPECT_EQ(result.size(), 4);
}
 
//==============================================================================
// Concat and Flatten Tests
//==============================================================================
 
TEST(StlConcat, Basic)
{
  std::vector<int> v1 = {1, 2, 3};
  std::vector<int> v2 = {4, 5, 6};
  
  auto result = stl_concat(v1, v2);
  
  EXPECT_EQ(result.size(), 6);
  EXPECT_EQ(result[0], 1);
  EXPECT_EQ(result[5], 6);
}
 
TEST(StlFlatten, Basic)
{
  std::vector<std::vector<int>> v = {{1, 2}, {3, 4}, {5}};
  
  auto result = stl_flatten(v);
  
  EXPECT_EQ(result.size(), 5);
  EXPECT_EQ(result[0], 1);
  EXPECT_EQ(result[4], 5);
}
 
TEST(StlFlatMap, Basic)
{
  std::vector<int> v = {1, 2, 3};
  auto result = stl_flat_map([](int x) {
    return std::vector<int>{x, x * 10};
  }, v);
  
  EXPECT_EQ(result.size(), 6);
  EXPECT_EQ(result[0], 1);
  EXPECT_EQ(result[1], 10);
  EXPECT_EQ(result[4], 3);
  EXPECT_EQ(result[5], 30);
}
 
//==============================================================================
// Grouping Tests
//==============================================================================
 
TEST(StlGroup, Basic)
{
  std::vector<int> v = {1, 1, 2, 2, 2, 3};
  
  auto result = stl_group(v);
  
  EXPECT_EQ(result.size(), 3);
  EXPECT_EQ(result[0].size(), 2);  // {1, 1}
  EXPECT_EQ(result[1].size(), 3);  // {2, 2, 2}
  EXPECT_EQ(result[2].size(), 1);  // {3}
}
 
TEST(StlGroupBy, Basic)
{
  std::vector<std::string> v = {"a", "bb", "c", "dd", "eee"};
  
  auto result = stl_group_by([](const std::string& s) { return s.length(); }, v);
  
  EXPECT_EQ(result.size(), 3);  // lengths 1, 2, 3
}
 
//==============================================================================
// Works with Different Container Types
//==============================================================================
 
TEST(StlFunctional, WorksWithList)
{
  std::list<int> l = {1, 2, 3, 4, 5};
  
  auto squares = stl_map([](int x) { return x * x; }, l);
  EXPECT_EQ(squares.size(), 5);
  EXPECT_EQ(squares[4], 25);
  
  int sum = stl_foldl(0, [](int acc, int x) { return acc + x; }, l);
  EXPECT_EQ(sum, 15);
  
  // foldr works with list (has rbegin/rend)
  int result = stl_foldr(0, [](int x, int acc) { return x - acc; }, l);
  EXPECT_EQ(result, 3);  // 1-(2-(3-(4-(5-0)))) = 1-(2-(3-(4-5))) = ...
}
 
TEST(StlFunctional, WorksWithDeque)
{
  std::deque<int> d = {1, 2, 3, 4, 5};
  
  auto evens = stl_filter([](int x) { return x % 2 == 0; }, d);
  EXPECT_EQ(evens.size(), 2);
}
 
//==============================================================================
// Combinatorics Tests
//==============================================================================
 
TEST(StlPermutations, Basic)
{
  std::vector<int> v = {1, 2, 3};
  auto perms = stl_permutations(v);
  
  EXPECT_EQ(perms.size(), 6);  // 3! = 6
}
 
TEST(StlPermutations, TraverseWithStop)
{
  std::vector<int> v = {1, 2, 3};
  int count = 0;
  
  bool completed = stl_traverse_permutations([&count](const auto&) {
    ++count;
    return count < 3;  // stop after 3
  }, v);
  
  EXPECT_FALSE(completed);
  EXPECT_EQ(count, 3);
}
 
TEST(StlCombinations, ChooseTwo)
{
  std::vector<int> v = {1, 2, 3, 4};
  auto combos = stl_combinations(2, v);
  
  // C(4,2) = 6
  EXPECT_EQ(combos.size(), 6);
  
  // Verify one combination
  EXPECT_EQ(combos[0][0], 1);
  EXPECT_EQ(combos[0][1], 2);
}
 
TEST(StlCombinations, ChooseThree)
{
  std::vector<int> v = {1, 2, 3, 4, 5};
  auto combos = stl_combinations(3, v);
  
  // C(5,3) = 10
  EXPECT_EQ(combos.size(), 10);
}
 
TEST(StlArrangements, ChooseTwo)
{
  std::vector<int> v = {1, 2, 3};
  auto arrs = stl_arrangements(2, v);
  
  // P(3,2) = 3!/(3-2)! = 6
  EXPECT_EQ(arrs.size(), 6);
}
 
TEST(StlCartesianProduct, Basic)
{
  std::vector<std::vector<int>> sets = {{1, 2}, {3, 4}};
  auto product = stl_cartesian_product(sets);
  
  // 2 * 2 = 4
  EXPECT_EQ(product.size(), 4);
}
 
TEST(StlPowerSet, Basic)
{
  std::vector<int> v = {1, 2, 3};
  auto ps = stl_power_set(v);
  
  // 2^3 = 8
  EXPECT_EQ(ps.size(), 8);
}
 
//==============================================================================
// Ruby/ML Operations Tests
//==============================================================================
 
TEST(StlSlidingWindow, Basic)
{
  std::vector<int> v = {1, 2, 3, 4, 5};
  auto windows = stl_sliding_window(3, v);
  
  EXPECT_EQ(windows.size(), 3);
  EXPECT_EQ(windows[0], (std::vector<int>{1, 2, 3}));
  EXPECT_EQ(windows[1], (std::vector<int>{2, 3, 4}));
  EXPECT_EQ(windows[2], (std::vector<int>{3, 4, 5}));
}
 
TEST(StlChunks, Basic)
{
  std::vector<int> v = {1, 2, 3, 4, 5};
  auto chunks = stl_chunks(2, v);
  
  EXPECT_EQ(chunks.size(), 3);
  EXPECT_EQ(chunks[0], (std::vector<int>{1, 2}));
  EXPECT_EQ(chunks[1], (std::vector<int>{3, 4}));
  EXPECT_EQ(chunks[2], (std::vector<int>{5}));
}
 
TEST(StlIntersperse, Basic)
{
  std::vector<int> v = {1, 2, 3};
  auto result = stl_intersperse(0, v);
  
  EXPECT_EQ(result, (std::vector<int>{1, 0, 2, 0, 3}));
}
 
TEST(StlSplitAt, Basic)
{
  std::vector<int> v = {1, 2, 3, 4, 5};
  auto [first, second] = stl_split_at(2, v);
  
  EXPECT_EQ(first, (std::vector<int>{1, 2}));
  EXPECT_EQ(second, (std::vector<int>{3, 4, 5}));
}
 
TEST(StlSpan, Basic)
{
  std::vector<int> v = {1, 2, 3, 10, 4, 5};
  auto [first, second] = stl_span([](int x) { return x < 10; }, v);
  
  EXPECT_EQ(first, (std::vector<int>{1, 2, 3}));
  EXPECT_EQ(second, (std::vector<int>{10, 4, 5}));
}
 
TEST(StlInit, Basic)
{
  std::vector<int> v = {1, 2, 3, 4, 5};
  auto result = stl_init(v);
  
  EXPECT_EQ(result, (std::vector<int>{1, 2, 3, 4}));
}
 
TEST(StlTail, Basic)
{
  std::vector<int> v = {1, 2, 3, 4, 5};
  auto result = stl_tail(v);
  
  EXPECT_EQ(result, (std::vector<int>{2, 3, 4, 5}));
}
 
TEST(StlTally, Basic)
{
  std::vector<int> v = {1, 2, 2, 3, 3, 3};
  auto result = stl_tally(v);
  
  EXPECT_EQ(result.size(), 3);
  EXPECT_EQ(result[0].first, 1);
  EXPECT_EQ(result[0].second, 1);
  EXPECT_EQ(result[1].first, 2);
  EXPECT_EQ(result[1].second, 2);
  EXPECT_EQ(result[2].first, 3);
  EXPECT_EQ(result[2].second, 3);
}
 
TEST(StlReject, Basic)
{
  std::vector<int> v = {1, 2, 3, 4, 5, 6};
  auto result = stl_reject([](int x) { return x % 2 == 0; }, v);
 
  EXPECT_EQ(result, (std::vector<int>{1, 3, 5}));
}
 
//==============================================================================
// Performance Tests - Large Containers (Hash Path)
//==============================================================================
 
TEST(StlDistinctPerformance, LargeContainerUsesHashPath)
{
  // Create container with 1000 elements, 100 distinct values
  std::vector<int> large;
  large.reserve(1000);
  for (int i = 0; i < 1000; ++i)
    large.push_back(i % 100);
 
  auto result = stl_distinct(large);
 
  EXPECT_EQ(result.size(), 100);
  // Verify order preserved (first occurrence)
  EXPECT_EQ(result[0], 0);
  EXPECT_EQ(result[1], 1);
  EXPECT_EQ(result[99], 99);
}
 
TEST(StlDistinctPerformance, VeryLargeContainer)
{
  // 10000 elements, 500 distinct
  std::vector<int> very_large;
  very_large.reserve(10000);
  for (int i = 0; i < 10000; ++i)
    very_large.push_back(i % 500);
 
  auto result = stl_distinct(very_large);
 
  EXPECT_EQ(result.size(), 500);
}
 
TEST(StlTallyPerformance, LargeContainerUsesHashPath)
{
  std::vector<int> large;
  large.reserve(1000);
  for (int i = 0; i < 1000; ++i)
    large.push_back(i % 100);
 
  auto result = stl_tally(large);
 
  EXPECT_EQ(result.size(), 100);
  // Each value appears 10 times
  for (const auto & [val, count] : result)
    EXPECT_EQ(count, 10);
}
 
TEST(StlGroupByPerformance, LargeContainerUsesHashPath)
{
  std::vector<int> large;
  large.reserve(1000);
  for (int i = 0; i < 1000; ++i)
    large.push_back(i);
 
  // Group by last digit
  auto result = stl_group_by([](int x) { return x % 10; }, large);
 
  EXPECT_EQ(result.size(), 10);
  for (const auto & [key, group] : result)
    EXPECT_EQ(group.size(), 100);
}
 
//==============================================================================
// Edge Cases
//==============================================================================
 
TEST(StlDistinctEdgeCases, EmptyContainer)
{
  std::vector<int> empty;
  auto result = stl_distinct(empty);
  EXPECT_TRUE(result.empty());
}
 
TEST(StlDistinctEdgeCases, SingleElement)
{
  std::vector<int> single = {42};
  auto result = stl_distinct(single);
  EXPECT_EQ(result.size(), 1);
  EXPECT_EQ(result[0], 42);
}
 
TEST(StlDistinctEdgeCases, AllSame)
{
  std::vector<int> all_same(100, 42);
  auto result = stl_distinct(all_same);
  EXPECT_EQ(result.size(), 1);
  EXPECT_EQ(result[0], 42);
}
 
TEST(StlDistinctEdgeCases, AllUnique)
{
  auto input = stl_range(0, 99);
  auto result = stl_distinct(input);
  EXPECT_EQ(result.size(), 100);
}
 
TEST(StlTallyEdgeCases, EmptyContainer)
{
  std::vector<int> empty;
  auto result = stl_tally(empty);
  EXPECT_TRUE(result.empty());
}
 
TEST(StlTallyEdgeCases, SingleElement)
{
  std::vector<int> single = {42};
  auto result = stl_tally(single);
  EXPECT_EQ(result.size(), 1);
  EXPECT_EQ(result[0].first, 42);
  EXPECT_EQ(result[0].second, 1);
}
 
TEST(StlGroupByEdgeCases, EmptyContainer)
{
  std::vector<int> empty;
  auto result = stl_group_by([](int x) { return x; }, empty);
  EXPECT_TRUE(result.empty());
}
 
TEST(StlGroupByEdgeCases, SingleElement)
{
  std::vector<int> single = {42};
  auto result = stl_group_by([](int x) { return x % 10; }, single);
  EXPECT_EQ(result.size(), 1);
  EXPECT_EQ(result[0].first, 2);
  EXPECT_EQ(result[0].second.size(), 1);
}
 
TEST(StlGroupByEdgeCases, AllSameKey)
{
  std::vector<int> v = {10, 20, 30, 40, 50};
  auto result = stl_group_by([](int x) { return x % 10; }, v);
  EXPECT_EQ(result.size(), 1);
  EXPECT_EQ(result[0].first, 0);
  EXPECT_EQ(result[0].second.size(), 5);
}
 
//==============================================================================
// Small Container Tests (Linear Path - threshold <= 64)
//==============================================================================
 
TEST(StlDistinctSmall, UsesLinearPath)
{
  // Exactly at threshold
  std::vector<int> at_threshold;
  for (int i = 0; i < 64; ++i)
    at_threshold.push_back(i % 32);
 
  auto result = stl_distinct(at_threshold);
  EXPECT_EQ(result.size(), 32);
}
 
TEST(StlTallySmall, UsesLinearPath)
{
  std::vector<int> small = {1, 2, 2, 3, 3, 3, 4, 4, 4, 4};
  auto result = stl_tally(small);
 
  EXPECT_EQ(result.size(), 4);
  EXPECT_EQ(result[0].second, 1);  // 1 appears once
  EXPECT_EQ(result[1].second, 2);  // 2 appears twice
  EXPECT_EQ(result[2].second, 3);  // 3 appears three times
  EXPECT_EQ(result[3].second, 4);  // 4 appears four times
}
 
//==============================================================================
// Custom Types Tests
//==============================================================================
 
namespace {
 
struct Point
{
  int x, y;
 
  bool operator==(const Point & other) const
  {
    return x == other.x && y == other.y;
  }
};
 
struct PointHash
{
  size_t operator()(const Point & p) const
  {
    return std::hash<int>{}(p.x) ^ (std::hash<int>{}(p.y) << 1);
  }
};
 
// Make Point hashable for std::unordered_set/map
} // anonymous namespace
 
namespace std {
template<>
struct hash<Point>
{
  size_t operator()(const Point & p) const
  {
    return hash<int>{}(p.x) ^ (hash<int>{}(p.y) << 1);
  }
};
} // namespace std
 
TEST(StlDistinctCustomType, PointsSmall)
{
  std::vector<Point> points = {{1, 2}, {3, 4}, {1, 2}, {5, 6}, {3, 4}};
  auto result = stl_distinct(points);
 
  EXPECT_EQ(result.size(), 3);
  EXPECT_EQ(result[0].x, 1);
  EXPECT_EQ(result[0].y, 2);
}
 
TEST(StlDistinctCustomType, PointsLarge)
{
  std::vector<Point> points;
  points.reserve(200);
  for (int i = 0; i < 200; ++i)
    points.push_back({i % 50, i % 25});
 
  auto result = stl_distinct(points);
  // 50 * 25 = 1250 possible, but we only have 200 elements with some repeats
  EXPECT_LE(result.size(), 200);
  EXPECT_GT(result.size(), 0);
}
 
TEST(StlTallyCustomType, Points)
{
  std::vector<Point> points = {{1, 2}, {3, 4}, {1, 2}, {5, 6}, {1, 2}};
  auto result = stl_tally(points);
 
  EXPECT_EQ(result.size(), 3);
  // Find the count for {1,2}
  auto it = std::find_if(result.begin(), result.end(),
                         [](const auto & p) { return p.first.x == 1 && p.first.y == 2; });
  ASSERT_NE(it, result.end());
  EXPECT_EQ(it->second, 3);
}
 
TEST(StlGroupByCustomType, PointsByQuadrant)
{
  std::vector<Point> points = {
    {1, 1}, {-1, 1}, {-1, -1}, {1, -1},
    {2, 3}, {-2, 3}, {-2, -3}, {2, -3}
  };
 
  auto quadrant = [](const Point & p) {
    if (p.x >= 0 && p.y >= 0) return 1;
    if (p.x < 0 && p.y >= 0) return 2;
    if (p.x < 0 && p.y < 0) return 3;
    return 4;
  };
 
  auto result = stl_group_by(quadrant, points);
 
  EXPECT_EQ(result.size(), 4);
  for (const auto & [quad, pts] : result)
    EXPECT_EQ(pts.size(), 2);
}
 
//==============================================================================
// Move Semantics and Forwarding Tests
//==============================================================================
 
namespace {
 
struct MoveTracker
{
  int value;
  static int move_count;
  static int copy_count;
 
  MoveTracker(int v = 0) : value(v) {}
 
  MoveTracker(const MoveTracker & other) : value(other.value)
  {
    ++copy_count;
  }
 
  MoveTracker(MoveTracker && other) noexcept : value(other.value)
  {
    other.value = -1;
    ++move_count;
  }
 
  MoveTracker & operator=(const MoveTracker & other)
  {
    value = other.value;
    ++copy_count;
    return *this;
  }
 
  MoveTracker & operator=(MoveTracker && other) noexcept
  {
    value = other.value;
    other.value = -1;
    ++move_count;
    return *this;
  }
 
  bool operator==(const MoveTracker & other) const
  {
    return value == other.value;
  }
 
  static void reset()
  {
    move_count = 0;
    copy_count = 0;
  }
};
 
int MoveTracker::move_count = 0;
int MoveTracker::copy_count = 0;
 
} // anonymous namespace
 
namespace std {
template<>
struct hash<MoveTracker>
{
  size_t operator()(const MoveTracker & m) const
  {
    return hash<int>{}(m.value);
  }
};
} // namespace std
 
TEST(StlMapForwarding, LambdaWithCapture)
{
  std::vector<int> v = {1, 2, 3};
  std::string prefix = "num_";
 
  auto result = stl_map([&prefix](int x) {
    return prefix + std::to_string(x);
  }, v);
 
  EXPECT_EQ(result[0], "num_1");
  EXPECT_EQ(result[1], "num_2");
  EXPECT_EQ(result[2], "num_3");
}
 
TEST(StlFilterForwarding, MutableLambda)
{
  std::vector<int> v = {1, 2, 3, 4, 5};
  int threshold = 3;
 
  // Mutable lambda that modifies captured state
  int call_count = 0;
  auto result = stl_filter([&call_count, threshold](int x) mutable {
    ++call_count;
    return x > threshold;
  }, v);
 
  EXPECT_EQ(result.size(), 2);
  EXPECT_EQ(call_count, 5);
}
 
TEST(StlFoldlForwarding, AccumulatorByValue)
{
  std::vector<std::string> words = {"hello", " ", "world"};
 
  auto result = stl_foldl(std::string{}, [](std::string acc, const std::string & w) {
    return acc + w;
  }, words);
 
  EXPECT_EQ(result, "hello world");
}
 
//==============================================================================
// Different Container Types
//==============================================================================
 
TEST(StlDistinctContainerTypes, List)
{
  std::list<int> l = {1, 2, 1, 3, 2, 4};
  auto result = stl_distinct(l);
  EXPECT_EQ(result.size(), 4);
}
 
TEST(StlDistinctContainerTypes, Deque)
{
  std::deque<int> d = {1, 2, 1, 3, 2, 4};
  auto result = stl_distinct(d);
  EXPECT_EQ(result.size(), 4);
}
 
TEST(StlTallyContainerTypes, List)
{
  std::list<int> l = {1, 2, 2, 3, 3, 3};
  auto result = stl_tally(l);
  EXPECT_EQ(result.size(), 3);
}
 
TEST(StlGroupByContainerTypes, List)
{
  std::list<std::string> l = {"a", "bb", "ccc", "dd", "e"};
  auto result = stl_group_by([](const std::string & s) { return s.length(); }, l);
  EXPECT_EQ(result.size(), 3);
}
 
//==============================================================================
// Order Preservation Tests
//==============================================================================
 
TEST(StlDistinctOrder, PreservesFirstOccurrence)
{
  std::vector<int> v = {5, 3, 5, 1, 3, 7, 1, 5};
  auto result = stl_distinct(v);
 
  ASSERT_EQ(result.size(), 4);
  EXPECT_EQ(result[0], 5);  // First occurrence
  EXPECT_EQ(result[1], 3);
  EXPECT_EQ(result[2], 1);
  EXPECT_EQ(result[3], 7);
}
 
TEST(StlDistinctOrder, PreservesFirstOccurrenceLarge)
{
  // Test with hash path
  std::vector<int> v;
  v.reserve(200);
  for (int i = 199; i >= 0; --i)
    v.push_back(i % 100);
 
  auto result = stl_distinct(v);
 
  ASSERT_EQ(result.size(), 100);
  // First occurrence of 99 is at index 0 (199 % 100 = 99)
  EXPECT_EQ(result[0], 99);
  // First occurrence of 98 is at index 1 (198 % 100 = 98)
  EXPECT_EQ(result[1], 98);
}
 
TEST(StlTallyOrder, PreservesFirstOccurrence)
{
  std::vector<int> v = {5, 3, 5, 1, 3, 7, 1, 5};
  auto result = stl_tally(v);
 
  ASSERT_EQ(result.size(), 4);
  EXPECT_EQ(result[0].first, 5);
  EXPECT_EQ(result[0].second, 3);
  EXPECT_EQ(result[1].first, 3);
  EXPECT_EQ(result[1].second, 2);
  EXPECT_EQ(result[2].first, 1);
  EXPECT_EQ(result[2].second, 2);
  EXPECT_EQ(result[3].first, 7);
  EXPECT_EQ(result[3].second, 1);
}
 
TEST(StlGroupByOrder, PreservesFirstOccurrence)
{
  std::vector<int> v = {15, 23, 31, 42, 54};
  auto result = stl_group_by([](int x) { return x % 10; }, v);
 
  ASSERT_EQ(result.size(), 5);
  // First key seen is 5 (from 15)
  EXPECT_EQ(result[0].first, 5);
  // Second key seen is 3 (from 23)
  EXPECT_EQ(result[1].first, 3);
}
 
//==============================================================================
// String Tests
//==============================================================================
 
TEST(StlDistinctStrings, Basic)
{
  std::vector<std::string> v = {"apple", "banana", "apple", "cherry", "banana"};
  auto result = stl_distinct(v);
 
  ASSERT_EQ(result.size(), 3);
  EXPECT_EQ(result[0], "apple");
  EXPECT_EQ(result[1], "banana");
  EXPECT_EQ(result[2], "cherry");
}
 
TEST(StlDistinctStrings, Large)
{
  std::vector<std::string> v;
  v.reserve(200);
  for (int i = 0; i < 200; ++i)
    v.push_back("str_" + std::to_string(i % 50));
 
  auto result = stl_distinct(v);
  EXPECT_EQ(result.size(), 50);
}
 
TEST(StlGroupByStrings, ByLength)
{
  std::vector<std::string> v = {"a", "bb", "ccc", "dd", "eee", "f"};
  auto result = stl_group_by([](const std::string & s) { return s.length(); }, v);
 
  EXPECT_EQ(result.size(), 3);
}
 
TEST(StlGroupByStrings, ByFirstChar)
{
  std::vector<std::string> v = {"apple", "apricot", "banana", "blueberry", "cherry"};
  auto result = stl_group_by([](const std::string & s) { return s[0]; }, v);
 
  EXPECT_EQ(result.size(), 3);  // a, b, c
}
 
//==============================================================================
// Boundary Tests (around threshold = 64)
//==============================================================================
 
TEST(StlDistinctBoundary, JustBelowThreshold)
{
  std::vector<int> v;
  for (int i = 0; i < 63; ++i)
    v.push_back(i % 30);
 
  auto result = stl_distinct(v);
  EXPECT_EQ(result.size(), 30);
}
 
TEST(StlDistinctBoundary, ExactlyAtThreshold)
{
  std::vector<int> v;
  for (int i = 0; i < 64; ++i)
    v.push_back(i % 30);
 
  auto result = stl_distinct(v);
  EXPECT_EQ(result.size(), 30);
}
 
TEST(StlDistinctBoundary, JustAboveThreshold)
{
  std::vector<int> v;
  for (int i = 0; i < 65; ++i)
    v.push_back(i % 30);
 
  auto result = stl_distinct(v);
  EXPECT_EQ(result.size(), 30);
}
 
//==============================================================================
// Composition Tests
//==============================================================================
 
TEST(StlComposition, DistinctThenMap)
{
  std::vector<int> v = {1, 2, 1, 3, 2, 4};
  auto distinct = stl_distinct(v);
  auto squared = stl_map([](int x) { return x * x; }, distinct);
 
  EXPECT_EQ(squared, (std::vector<int>{1, 4, 9, 16}));
}
 
TEST(StlComposition, FilterThenDistinct)
{
  std::vector<int> v = {1, 2, 3, 4, 5, 6, 1, 2, 3};
  auto evens = stl_filter([](int x) { return x % 2 == 0; }, v);
  auto unique_evens = stl_distinct(evens);
 
  EXPECT_EQ(unique_evens, (std::vector<int>{2, 4, 6}));
}
 
TEST(StlComposition, GroupByThenMap)
{
  std::vector<int> v = {1, 2, 3, 4, 5, 6};
  auto groups = stl_group_by([](int x) { return x % 2; }, v);
  auto sums = stl_map([](const auto & p) {
    return std::make_pair(p.first, stl_foldl(0, std::plus<int>{}, p.second));
  }, groups);
 
  EXPECT_EQ(sums.size(), 2);
}
 
//==============================================================================
// forward_list Compatibility Tests (containers without size())
//==============================================================================
 
#include <forward_list>
 
TEST(StlForwardListCompat, Map)
{
  std::forward_list<int> fl = {1, 2, 3, 4, 5};
  auto result = stl_map([](int x) { return x * 2; }, fl);
 
  EXPECT_EQ(result.size(), 5);
  EXPECT_EQ(result[0], 2);
  EXPECT_EQ(result[4], 10);
}
 
TEST(StlForwardListCompat, Filter)
{
  std::forward_list<int> fl = {1, 2, 3, 4, 5, 6};
  auto result = stl_filter([](int x) { return x % 2 == 0; }, fl);
 
  EXPECT_EQ(result.size(), 3);
  EXPECT_EQ(result[0], 2);
}
 
TEST(StlForwardListCompat, Foldl)
{
  std::forward_list<int> fl = {1, 2, 3, 4, 5};
  int sum = stl_foldl(0, [](int acc, int x) { return acc + x; }, fl);
 
  EXPECT_EQ(sum, 15);
}
 
TEST(StlForwardListCompat, Distinct)
{
  std::forward_list<int> fl = {1, 2, 1, 3, 2, 4};
  auto result = stl_distinct(fl);
 
  EXPECT_EQ(result.size(), 4);
}
 
TEST(StlForwardListCompat, Tally)
{
  std::forward_list<int> fl = {1, 2, 2, 3, 3, 3};
  auto result = stl_tally(fl);
 
  EXPECT_EQ(result.size(), 3);
}
 
TEST(StlForwardListCompat, GroupBy)
{
  std::forward_list<int> fl = {1, 2, 3, 4, 5, 6};
  auto result = stl_group_by([](int x) { return x % 2; }, fl);
 
  EXPECT_EQ(result.size(), 2);
}
 
TEST(StlForwardListCompat, Last)
{
  std::forward_list<int> fl = {1, 2, 3, 4, 5};
  auto result = stl_last(fl);
 
  ASSERT_TRUE(result.has_value());
  EXPECT_EQ(*result, 5);
}
 
TEST(StlForwardListCompat, TakeLast)
{
  std::forward_list<int> fl = {1, 2, 3, 4, 5};
  auto result = stl_take_last(3, fl);
 
  EXPECT_EQ(result.size(), 3);
  EXPECT_EQ(result[0], 3);
  EXPECT_EQ(result[2], 5);
}
 
TEST(StlForwardListCompat, Drop)
{
  std::forward_list<int> fl = {1, 2, 3, 4, 5};
  auto result = stl_drop(2, fl);
 
  EXPECT_EQ(result.size(), 3);
  EXPECT_EQ(result[0], 3);
}
 
//==============================================================================
// Non-Hashable Type Tests (uses linear path only)
//==============================================================================
 
namespace {
 
// A type that is NOT hashable (no std::hash specialization)
struct NonHashable
{
  int x, y;
 
  bool operator==(const NonHashable & other) const
  {
    return x == other.x && y == other.y;
  }
};
 
} // anonymous namespace
 
TEST(StlNonHashable, DistinctSmall)
{
  std::vector<NonHashable> v = {{1, 2}, {3, 4}, {1, 2}, {5, 6}};
  auto result = stl_distinct(v);
 
  EXPECT_EQ(result.size(), 3);
}
 
TEST(StlNonHashable, DistinctLarge)
{
  // Even with large container, non-hashable types use linear path
  std::vector<NonHashable> v;
  v.reserve(200);
  for (int i = 0; i < 200; ++i)
    v.push_back({i % 50, i % 25});
 
  auto result = stl_distinct(v);
 
  EXPECT_GT(result.size(), 0);
  EXPECT_LE(result.size(), 200);
}
 
TEST(StlNonHashable, TallySmall)
{
  std::vector<NonHashable> v = {{1, 2}, {3, 4}, {1, 2}, {1, 2}};
  auto result = stl_tally(v);
 
  EXPECT_EQ(result.size(), 2);
  // Find the count for {1,2}
  auto it = std::find_if(result.begin(), result.end(),
                         [](const auto & p) { return p.first.x == 1 && p.first.y == 2; });
  ASSERT_NE(it, result.end());
  EXPECT_EQ(it->second, 3);
}
 
TEST(StlNonHashable, GroupByWithNonHashableKey)
{
  // Group by a non-hashable key type
  std::vector<int> v = {1, 2, 3, 4, 5, 6, 7, 8};
 
  // Key function returns NonHashable
  auto result = stl_group_by([](int x) {
    return NonHashable{x % 2, x % 3};
  }, v);
 
  // With modulo (2,3), we can have up to 6 different keys
  EXPECT_GT(result.size(), 0);
  EXPECT_LE(result.size(), 6);
}
 
//==============================================================================
// Stateful Callable Tests (verifies fix for std::forward in loops)
//==============================================================================
 
namespace {
 
struct StatefulCallable
{
  int call_count = 0;
  int threshold;
 
  explicit StatefulCallable(int t) : threshold(t) {}
 
  bool operator()(int x)
  {
    ++call_count;
    return x > threshold;
  }
};
 
struct StatefulMapper
{
  int multiplier;
  int call_count = 0;
 
  explicit StatefulMapper(int m) : multiplier(m) {}
 
  int operator()(int x)
  {
    ++call_count;
    return x * multiplier;
  }
};
 
} // anonymous namespace
 
TEST(StlStatefulCallable, FilterPreservesState)
{
  std::vector<int> v = {1, 2, 3, 4, 5};
 
  // Use a stateful callable
  StatefulCallable pred(3);
  auto result = stl_filter(pred, v);
 
  EXPECT_EQ(result.size(), 2);
  EXPECT_EQ(result[0], 4);
  EXPECT_EQ(result[1], 5);
}
 
TEST(StlStatefulCallable, MapPreservesState)
{
  std::vector<int> v = {1, 2, 3};
 
  StatefulMapper mapper(10);
  auto result = stl_map(mapper, v);
 
  EXPECT_EQ(result.size(), 3);
  EXPECT_EQ(result[0], 10);
  EXPECT_EQ(result[1], 20);
  EXPECT_EQ(result[2], 30);
}
 
TEST(StlStatefulCallable, ForEachPreservesState)
{
  std::vector<int> v = {1, 2, 3, 4, 5};
 
  int sum = 0;
  int call_count = 0;
 
  // Lambda that modifies external state
  stl_for_each([&sum, &call_count](int x) {
    sum += x;
    ++call_count;
  }, v);
 
  EXPECT_EQ(sum, 15);
  EXPECT_EQ(call_count, 5);
}
 
TEST(StlStatefulCallable, AllPreservesState)
{
  std::vector<int> v = {2, 4, 6, 8, 10};
 
  int call_count = 0;
  bool result = stl_all([&call_count](int x) {
    ++call_count;
    return x % 2 == 0;
  }, v);
 
  EXPECT_TRUE(result);
  EXPECT_EQ(call_count, 5);
}
 
TEST(StlStatefulCallable, ExistsStopsEarly)
{
  std::vector<int> v = {1, 2, 3, 4, 5};
 
  int call_count = 0;
  bool result = stl_exists([&call_count](int x) {
    ++call_count;
    return x == 2;  // Found at second element
  }, v);
 
  EXPECT_TRUE(result);
  EXPECT_EQ(call_count, 2);  // Should stop after finding element
}
 
//==============================================================================
// Edge Cases for Empty Containers
//==============================================================================
 
TEST(StlEmptyContainer, LastReturnsNullopt)
{
  std::vector<int> empty;
  auto result = stl_last(empty);
  EXPECT_FALSE(result.has_value());
}
 
TEST(StlEmptyContainer, MinReturnsNullopt)
{
  std::vector<int> empty;
  auto result = stl_min(empty);
  EXPECT_FALSE(result.has_value());
}
 
TEST(StlEmptyContainer, MaxReturnsNullopt)
{
  std::vector<int> empty;
  auto result = stl_max(empty);
  EXPECT_FALSE(result.has_value());
}
 
TEST(StlEmptyContainer, ProductReturnsZero)
{
  std::vector<int> empty;
  auto result = stl_product(empty);
  EXPECT_EQ(result, 0);
}
 
TEST(StlEmptyContainer, SumReturnsZero)
{
  std::vector<int> empty;
  auto result = stl_sum(empty);
  EXPECT_EQ(result, 0);
}
 
TEST(StlEmptyContainer, ScanLeftReturnsInit)
{
  std::vector<int> empty;
  auto result = stl_scan_left(42, [](int a, int b) { return a + b; }, empty);
 
  EXPECT_EQ(result.size(), 1);
  EXPECT_EQ(result[0], 42);
}
 
TEST(StlEmptyContainer, ScanRightReturnsInit)
{
  std::vector<int> empty;
  auto result = stl_scan_right(42, [](int a, int b) { return a + b; }, empty);
 
  EXPECT_EQ(result.size(), 1);
  EXPECT_EQ(result[0], 42);
}
 
TEST(StlEmptyContainer, InterspersReturnsEmpty)
{
  std::vector<int> empty;
  auto result = stl_intersperse(0, empty);
  EXPECT_TRUE(result.empty());
}
 
TEST(StlEmptyContainer, SlidingWindowReturnsEmpty)
{
  std::vector<int> empty;
  auto result = stl_sliding_window(3, empty);
  EXPECT_TRUE(result.empty());
}
 
TEST(StlEmptyContainer, ChunksReturnsEmpty)
{
  std::vector<int> empty;
  auto result = stl_chunks(3, empty);
  EXPECT_TRUE(result.empty());
}
 
//==============================================================================
// Power Set Overflow Protection Test
//==============================================================================
 
TEST(StlPowerSetOverflow, ThrowsForLargeContainer)
{
  // Create a container with 64 elements (would overflow 2^64)
  std::vector<int> large(64);
  std::iota(large.begin(), large.end(), 0);
 
  EXPECT_THROW(stl_power_set(large), std::overflow_error);
}
 
TEST(StlPowerSetOverflow, WorksForSmallContainer)
{
  std::vector<int> small = {1, 2, 3, 4, 5};
  auto result = stl_power_set(small);
 
  EXPECT_EQ(result.size(), 32);  // 2^5 = 32
}
 
// Main
int main(int argc, char **argv)
{
  ::testing::InitGoogleTest(&argc, argv);
  return RUN_ALL_TESTS();
}