[llvm] [libc] Add invoke (PR #65753)

[via llvm-commits]

================
@@ -0,0 +1,90 @@
+//===-- invoke_result type_traits -------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+#ifndef LLVM_LIBC_SRC_SUPPORT_CPP_TYPE_TRAITS_INVOKE_RESULT_H
+#define LLVM_LIBC_SRC_SUPPORT_CPP_TYPE_TRAITS_INVOKE_RESULT_H
+
+#include "src/__support/CPP/type_traits/decay.h"
+#include "src/__support/CPP/type_traits/enable_if.h"
+#include "src/__support/CPP/type_traits/false_type.h"
+#include "src/__support/CPP/type_traits/is_base_of.h"
+#include "src/__support/CPP/type_traits/is_function.h"
+#include "src/__support/CPP/type_traits/true_type.h"
+#include "src/__support/CPP/utility/declval.h"
+#include "src/__support/CPP/utility/forward.h"
+
+// BEWARE : this implementation is not fully conformant as it doesn't take
+// `cpp::reference_wrapper` into account.
+
+namespace __llvm_libc::cpp {
+
+// invoke_result
+
+namespace detail {
+template <class T> struct is_reference_wrapper : cpp::false_type {};
+
+// Disable specialization on `cpp::reference_wrapper` as it is not yet
+// implemented.
+
+// template <class U> struct
+// is_reference_wrapper<cpp::reference_wrapper<U>> : cpp::true_type {};
+
+template <class T> struct invoke_impl {
+  template <class F, class... Args>
+  static auto call(F &&f, Args &&...args)
+      -> decltype(cpp::forward<F>(f)(cpp::forward<Args>(args)...));
+};
+
+template <class B, class MT> struct invoke_impl<MT B::*> {
+  template <class T, class Td = cpp::decay_t<T>,
+            class = cpp::enable_if_t<cpp::is_base_of_v<B, Td>>>
+  static auto get(T &&t) -> T &&;
+
+  template <class T, class Td = cpp::decay_t<T>,
+            class = cpp::enable_if_t<is_reference_wrapper<Td>::value>>
+  static auto get(T &&t) -> decltype(t.get());
+
+  template <class T, class Td = cpp::decay_t<T>,
+            class = cpp::enable_if_t<!cpp::is_base_of_v<B, Td>>,
+            class = cpp::enable_if_t<!is_reference_wrapper<Td>::value>>
+  static auto get(T &&t) -> decltype(*cpp::forward<T>(t));
+
+  template <class T, class... Args, class MT1,
+            class = cpp::enable_if_t<cpp::is_function_v<MT1>>>
+  static auto call(MT1 B::*pmf, T &&t, Args &&...args)
+      -> decltype((invoke_impl::get(cpp::forward<T>(t)).*
+                   pmf)(cpp::forward<Args>(args)...));
+
+  template <class T>
+  static auto call(MT B::*pmd, T &&t)
+      -> decltype(invoke_impl::get(cpp::forward<T>(t)).*pmd);
+};
+
+template <class F, class... Args, class Fd = typename cpp::decay_t<F>>
+auto INVOKE(F &&f, Args &&...args)
----------------
lntue wrote:

why is this all caps?

https://github.com/llvm/llvm-project/pull/65753