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https://github.com/carbon-language/carbon-lang.git
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Jon Meow
20728dbd3a
This modifies scripts/check_header_guards.py to add the CARBON_ prefix; everything else is pre-commit.
35 lines
1.3 KiB
C++
35 lines
1.3 KiB
C++
// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
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// Exceptions. See /LICENSE for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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#ifndef CARBON_COMMON_METAPROGRAMMING_H_
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#define CARBON_COMMON_METAPROGRAMMING_H_
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#include <type_traits>
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namespace Carbon {
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// C++17-compatible emulation of a C++20 `requires` expression, which queries
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// whether a given expression is well-formed. The syntax is best explained
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// in terms of an example:
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//
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// template <typename T>
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// static constexpr bool IsStreamableToRawOstream =
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// Requires<const T, llvm::raw_ostream>(
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// [](auto&& t, auto&& out) -> decltype(out << t) {});
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//
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// The expression enclosed in `decltype` is the expression whose validity the
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// trait queries. The lambda parameters declare the names that are used in
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// that expression, and the types of those names are specified by the
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// corresponding template arguments of the `Requires` call. The lambda
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// parameters should always have type `auto&&`, and the template arguments
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// should not have `&` or `&&` qualifiers.
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template <typename... T, typename F>
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constexpr auto Requires(F /* f */) -> bool {
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return std::is_invocable_v<F, T...>;
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}
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} // namespace Carbon
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#endif // CARBON_COMMON_METAPROGRAMMING_H_
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