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AK: Add rvalue-ref qualifiers for Optional's value() and value_or()

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This avoids a value copy when calling value() or value_or() on a
temporary Optional. This is very common when using the HashMap::get()
API like this:

    auto value = hash_map.get(key).value_or(fallback_value);
This commit is contained in:
Andreas Kling 2021-09-04 00:44:10 +02:00
parent 0b36499f46
commit 7dda773426
2 changed files with 36 additions and 3 deletions
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21
Tests/AK/TestOptional.cpp
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@ -34,6 +34,27 @@ TEST_CASE(move_optional)
EXPECT_EQ(x.has_value(), false);
}
TEST_CASE(optional_rvalue_ref_qualified_getters)
{
struct DontCopyMe {
DontCopyMe() { }
~DontCopyMe() = default;
DontCopyMe(DontCopyMe&&) = default;
DontCopyMe& operator=(DontCopyMe&&) = default;
DontCopyMe(DontCopyMe const&) = delete;
DontCopyMe& operator=(DontCopyMe const&) = delete;
int x { 13 };
};
auto make_an_optional = []() -> Optional<DontCopyMe> {
return DontCopyMe {};
};
EXPECT_EQ(make_an_optional().value().x, 13);
EXPECT_EQ(make_an_optional().value_or(DontCopyMe {}).x, 13);
}
TEST_CASE(optional_leak_1)
{
struct Structure {