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Telegram/ThirdParty/range-v3/test/view/generate_n.cpp

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+// Range v3 library
+//
+//  Copyright Eric Niebler 2014-present
+//
+//  Use, modification and distribution is subject to the
+//  Boost Software License, Version 1.0. (See accompanying
+//  file LICENSE_1_0.txt or copy at
+//  http://www.boost.org/LICENSE_1_0.txt)
+//
+// Project home: https://github.com/ericniebler/range-v3
+
+#include <range/v3/core.hpp>
+#include <range/v3/view/drop_exactly.hpp>
+#include <range/v3/view/generate_n.hpp>
+#include "../simple_test.hpp"
+#include "../test_utils.hpp"
+
+namespace views = ranges::views;
+
+int main()
+{
+    // Test for constant generator functions
+    {
+        int i = 0, j = 1;
+        auto fib = views::generate_n([&]()->int{int tmp = i; i += j; std::swap(i, j); return tmp;}, 10);
+        CPP_assert(ranges::input_range<decltype(fib)> && ranges::view_<decltype(fib)>);
+        check_equal(fib, {0,1,1,2,3,5,8,13,21,34});
+    }
+
+    // Test for mutable-only generator functions
+    {
+        int i = 0, j = 1;
+        auto fib = views::generate_n([=]()mutable->int{int tmp = i; i += j; std::swap(i, j); return tmp;}, 10);
+        CPP_assert(ranges::input_range<decltype(fib)> && ranges::view_<decltype(fib)>);
+        check_equal(fib, {0,1,1,2,3,5,8,13,21,34});
+        // The generator cannot be called when it's const-qualified, so "fib const"
+        // does not model View.
+        CPP_assert(!ranges::view_<decltype(fib) const>);
+    }
+
+    // Test for generator functions that return move-only types
+    // https://github.com/ericniebler/range-v3/issues/905
+    {
+        char str[] = "gi";
+        auto rng = views::generate_n([&]{str[0]++; return MoveOnlyString{str};}, 2);
+        CPP_assert(ranges::input_range<decltype(rng)> && ranges::view_<decltype(rng)>);
+        auto i = rng.begin();
+        CHECK(bool(*i == MoveOnlyString{"hi"}));
+        CHECK(bool(*i == MoveOnlyString{"hi"}));
+        CHECK(bool(*rng.begin() == MoveOnlyString{"hi"}));
+        CHECK(bool(*rng.begin() == MoveOnlyString{"hi"}));
+        CPP_assert(ranges::input_range<decltype(rng)> && ranges::view_<decltype(rng)>);
+        check_equal(rng, {MoveOnlyString{"hi"}, MoveOnlyString{"ii"}});
+        static_assert(std::is_same<ranges::range_reference_t<decltype(rng)>, MoveOnlyString &&>::value, "");
+    }
+
+    // Test for generator functions that return internal references
+    // https://github.com/ericniebler/range-v3/issues/807
+    {
+        int i = 42;
+        auto rng = views::generate_n([i]{return &i;}, 2);
+        auto rng2 = std::move(rng);
+        auto it = rng2.begin();
+        auto p = *it;
+        auto p2 = *++it;
+        CHECK(p == p2);
+    }
+
+    // Test that we only call the function once for each dereferenceable position
+    // https://github.com/ericniebler/range-v3/issues/819
+    {
+        int i = 0;
+        auto rng = views::generate_n([&i]{return ++i;}, 2);
+        auto rng2 = std::move(rng);
+        auto it = rng2.begin();
+        CHECK(i == 0);
+        CHECK(*it == 1);
+        CHECK(i == 1);
+        ++it;
+        CHECK(i == 1);
+        CHECK(*it == 2);
+        CHECK(i == 2);
+    }
+
+    // Test view_interaface sized()-based empty()
+    // https://github.com/ericniebler/range-v3/issues/1147
+    {
+        int i = 0;
+        auto rng = views::generate_n([&i]{return ++i;}, 2);
+        CHECK(!rng.empty());
+    }
+
+
+    // Test that skipping past positions works correctly
+    // https://github.com/ericniebler/range-v3/issues/1258
+    {
+        auto fib = [p = std::make_pair(0, 1)]() mutable -> int {
+            auto a = p.first;
+            p = {p.second, p.first + p.second};
+            return a;
+        };
+
+        auto rng = ranges::views::generate_n(fib, 8)
+            | ranges::views::drop_exactly(3);
+
+        check_equal(rng, {2,3,5,8,13});
+    }
+
+    return test_result();
+}