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AK: Make the constexpr StringView methods actually constexpr

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Also add some tests to ensure that they _remain_ constexpr.
In general, any runtime assertions, weirdo C casts, pointer aliasing,
and such shenanigans should be gated behind the (helpfully newly added)
AK::is_constant_evaluated() function when the intention is to write
constexpr-capable code.
a.k.a. deliver promises of constexpr-ness :P
This commit is contained in:
Ali Mohammad Pur 2021-06-27 22:41:38 +04:30 committed by Linus Groh
parent 67d1b28b97
commit 37b0f55104
Notes: sideshowbarker 2024-07-18 11:26:45 +09:00 
Author: https://github.com/alimpfard
Commit: https://github.com/SerenityOS/serenity/commit/37b0f551042
Pull-request: https://github.com/SerenityOS/serenity/pull/8274
Reviewed-by: https://github.com/linusg ✅
3 changed files with 41 additions and 4 deletions
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10
AK/StdLibExtras.h
View file

@ -116,6 +116,15 @@ constexpr decltype(auto) to_underlying(V value) requires(IsEnum<V>)
return static_cast<UnderlyingType<V>>(value); return static_cast<UnderlyingType<V>>(value);
} }
constexpr bool is_constant_evaluated()
{
#if __has_builtin(__builtin_is_constant_evaluated)
return __builtin_is_constant_evaluated();
#else
return false;
#endif
}
} }
using AK::array_size; using AK::array_size;
@ -123,6 +132,7 @@ using AK::ceil_div;
using AK::clamp; using AK::clamp;
using AK::exchange; using AK::exchange;
using AK::forward; using AK::forward;
using AK::is_constant_evaluated;
using AK::max; using AK::max;
using AK::min; using AK::min;
using AK::RawPtr; using AK::RawPtr;

10
AK/StringView.h
View file

@ -24,7 +24,8 @@ public:
: m_characters(characters) : m_characters(characters)
, m_length(length) , m_length(length)
{ {
VERIFY(!Checked<uintptr_t>::addition_would_overflow((uintptr_t)characters, length)); if (!is_constant_evaluated())
VERIFY(!Checked<uintptr_t>::addition_would_overflow((uintptr_t)characters, length));
} }
ALWAYS_INLINE StringView(const unsigned char* characters, size_t length) ALWAYS_INLINE StringView(const unsigned char* characters, size_t length)
: m_characters((const char*)characters) : m_characters((const char*)characters)
@ -93,7 +94,8 @@ public:
[[nodiscard]] constexpr StringView substring_view(size_t start, size_t length) const [[nodiscard]] constexpr StringView substring_view(size_t start, size_t length) const
{ {
VERIFY(start + length <= m_length); if (!is_constant_evaluated())
VERIFY(start + length <= m_length);
return { m_characters + start, length }; return { m_characters + start, length };
} }
@ -158,7 +160,7 @@ public:
[[nodiscard]] StringView substring_view_starting_from_substring(const StringView& substring) const; [[nodiscard]] StringView substring_view_starting_from_substring(const StringView& substring) const;
[[nodiscard]] StringView substring_view_starting_after_substring(const StringView& substring) const; [[nodiscard]] StringView substring_view_starting_after_substring(const StringView& substring) const;
bool operator==(const char* cstring) const constexpr bool operator==(const char* cstring) const
{ {
if (is_null()) if (is_null())
return !cstring; return !cstring;
@ -175,7 +177,7 @@ public:
return !*cp; return !*cp;
} }
bool operator!=(const char* cstring) const constexpr bool operator!=(const char* cstring) const
{ {
return !(*this == cstring); return !(*this == cstring);
} }

25
Tests/AK/TestStringView.cpp
View file

@ -177,3 +177,28 @@ TEST_CASE(split_view)
EXPECT_EQ(test_string_view.split_view_if(predicate), Vector<StringView>({ "a", "b", "c", "d" })); EXPECT_EQ(test_string_view.split_view_if(predicate), Vector<StringView>({ "a", "b", "c", "d" }));
EXPECT_EQ(test_string_view.split_view_if(predicate, true), Vector<StringView>({ "a", "", "b", "c", "d" })); EXPECT_EQ(test_string_view.split_view_if(predicate, true), Vector<StringView>({ "a", "", "b", "c", "d" }));
} }
TEST_CASE(constexpr_stuff)
{
#define do_test() \
static_assert(test_constexpr.length() == 3); \
static_assert(!test_constexpr.is_empty()); \
static_assert(test_constexpr.is_one_of("foo", "bar", "baz")); \
static_assert(test_constexpr.is_one_of("foo"sv, "bar"sv, "baz"sv)); \
static_assert(test_constexpr != "fob"sv); \
static_assert(test_constexpr != "fob"); \
static_assert(test_constexpr.substring_view(1).is_one_of("oo"sv));
{
// Can initialize from ""sv.
constexpr StringView test_constexpr { "foo"sv };
do_test();
}
{
// Can initialize from char const*.
constexpr StringView test_constexpr { "foo" };
do_test();
}
#undef do_test
}