Reland "Move webrtc/{base => rtc_base}" (https://codereview.webrtc.org/2877023002)
Reland the base->rtc_base without adding stub headers (will be
done in follow-up CL). This preserves git blame history of all files.
BUG=webrtc:7634
NOTRY=True
TBR=kwiberg@webrtc.org
Change-Id: Iea3bb6f3f67b8374c96337b63e8f5aa3e6181012
Reviewed-on: https://chromium-review.googlesource.com/554611
Reviewed-by: Henrik Kjellander <kjellander@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#18821}diff --git a/webrtc/rtc_base/function_view.h b/webrtc/rtc_base/function_view.h
new file mode 100644
index 0000000..56964a6
--- /dev/null
+++ b/webrtc/rtc_base/function_view.h
@@ -0,0 +1,130 @@
+/*
+ * Copyright 2016 The WebRTC Project Authors. All rights reserved.
+ *
+ * Use of this source code is governed by a BSD-style license
+ * that can be found in the LICENSE file in the root of the source
+ * tree. An additional intellectual property rights grant can be found
+ * in the file PATENTS. All contributing project authors may
+ * be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef WEBRTC_RTC_BASE_FUNCTION_VIEW_H_
+#define WEBRTC_RTC_BASE_FUNCTION_VIEW_H_
+
+#include <type_traits>
+#include <utility>
+
+#include "webrtc/base/checks.h"
+
+// Just like std::function, FunctionView will wrap any callable and hide its
+// actual type, exposing only its signature. But unlike std::function,
+// FunctionView doesn't own its callable---it just points to it. Thus, it's a
+// good choice mainly as a function argument when the callable argument will
+// not be called again once the function has returned.
+//
+// Its constructors are implicit, so that callers won't have to convert lambdas
+// and other callables to FunctionView<Blah(Blah, Blah)> explicitly. This is
+// safe because FunctionView is only a reference to the real callable.
+//
+// Example use:
+//
+// void SomeFunction(rtc::FunctionView<int(int)> index_transform);
+// ...
+// SomeFunction([](int i) { return 2 * i + 1; });
+//
+// Note: FunctionView is tiny (essentially just two pointers) and trivially
+// copyable, so it's probably cheaper to pass it by value than by const
+// reference.
+
+namespace rtc {
+
+template <typename T>
+class FunctionView; // Undefined.
+
+template <typename RetT, typename... ArgT>
+class FunctionView<RetT(ArgT...)> final {
+ public:
+ // Constructor for lambdas and other callables; it accepts every type of
+ // argument except those noted in its enable_if call.
+ template <
+ typename F,
+ typename std::enable_if<
+ // Not for function pointers; we have another constructor for that
+ // below.
+ !std::is_function<typename std::remove_pointer<
+ typename std::remove_reference<F>::type>::type>::value &&
+
+ // Not for nullptr; we have another constructor for that below.
+ !std::is_same<std::nullptr_t,
+ typename std::remove_cv<F>::type>::value &&
+
+ // Not for FunctionView objects; we have another constructor for that
+ // (the implicitly declared copy constructor).
+ !std::is_same<FunctionView,
+ typename std::remove_cv<typename std::remove_reference<
+ F>::type>::type>::value>::type* = nullptr>
+ FunctionView(F&& f)
+ : call_(CallVoidPtr<typename std::remove_reference<F>::type>) {
+ f_.void_ptr = &f;
+ }
+
+ // Constructor that accepts function pointers. If the argument is null, the
+ // result is an empty FunctionView.
+ template <
+ typename F,
+ typename std::enable_if<std::is_function<typename std::remove_pointer<
+ typename std::remove_reference<F>::type>::type>::value>::type* =
+ nullptr>
+ FunctionView(F&& f)
+ : call_(f ? CallFunPtr<typename std::remove_pointer<F>::type> : nullptr) {
+ f_.fun_ptr = reinterpret_cast<void (*)()>(f);
+ }
+
+ // Constructor that accepts nullptr. It creates an empty FunctionView.
+ template <typename F,
+ typename std::enable_if<std::is_same<
+ std::nullptr_t,
+ typename std::remove_cv<F>::type>::value>::type* = nullptr>
+ FunctionView(F&& f) : call_(nullptr) {}
+
+ // Default constructor. Creates an empty FunctionView.
+ FunctionView() : call_(nullptr) {}
+
+ RetT operator()(ArgT... args) const {
+ RTC_DCHECK(call_);
+ return call_(f_, std::forward<ArgT>(args)...);
+ }
+
+ // Returns true if we have a function, false if we don't (i.e., we're null).
+ explicit operator bool() const { return !!call_; }
+
+ private:
+ union VoidUnion {
+ void* void_ptr;
+ void (*fun_ptr)();
+ };
+
+ template <typename F>
+ static RetT CallVoidPtr(VoidUnion vu, ArgT... args) {
+ return (*static_cast<F*>(vu.void_ptr))(std::forward<ArgT>(args)...);
+ }
+ template <typename F>
+ static RetT CallFunPtr(VoidUnion vu, ArgT... args) {
+ return (reinterpret_cast<typename std::add_pointer<F>::type>(vu.fun_ptr))(
+ std::forward<ArgT>(args)...);
+ }
+
+ // A pointer to the callable thing, with type information erased. It's a
+ // union because we have to use separate types depending on if the callable
+ // thing is a function pointer or something else.
+ VoidUnion f_;
+
+ // Pointer to a dispatch function that knows the type of the callable thing
+ // that's stored in f_, and how to call it. A FunctionView object is empty
+ // (null) iff call_ is null.
+ RetT (*call_)(VoidUnion, ArgT...);
+};
+
+} // namespace rtc
+
+#endif // WEBRTC_RTC_BASE_FUNCTION_VIEW_H_