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base / scoped_observation_traits.h [blame]
// Copyright 2022 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef BASE_SCOPED_OBSERVATION_TRAITS_H_
#define BASE_SCOPED_OBSERVATION_TRAITS_H_
namespace base {
// `ScopedObservationTraits` is used to control the behavior of
// `ScopedObservation` on sources without AddObserver()/RemoveObserver()
// methods.
//
// The implementation of `ScopedObservation<Source, Observer>` will look up the
// most specialized version of `ScopedObservationTraits<Source, Observer>` and
// use the corresponding `Traits::AddObserver` and `Traits::RemoveObserver`.
//
// The default specialization takes care of any Source that exposes
// `AddObserver(Observer*)` and `RemoveObserver(Observer*)` methods -- if that's
// the case, then `ScopedObservation<Source, Observer>` will work out of the
// box.
//
// However, if your `CustomSource` features custom method names -- say,
// `AddFoo(FooObserver*)` and `RemoveFoo(FooObserver*)`, then you'll have to
// define a new traits specialization like this:
//
// `custom_source.h`:
// #include "base/scoped_observation_traits.h"
//
// class FooObserver;
// class CustomSource {
// public:
// void AddFoo(FooObserver*);
// void RemoveFoo(FooObserver*);
// };
//
// namespace base {
//
// template<>
// struct ScopedObservationTraits<CustomSource, FooObserver> {
// static void AddObserver(CustomSource* source,
// FooObserver* observer) {
// source->AddFoo(observer);
// }
// static void RemoveObserver(CustomSource* source,
// FooObserver* observer) {
// source->RemoveFoo(observer);
// }
// };
//
// } // namespace base
//
// `some_important_file.cc`:
// // Now this works out of the box.
// base::ScopedObservation<CustomSource, FooObserver> obs...
//
template <class Source, class Observer>
struct ScopedObservationTraits {
static_assert(
requires(Source& source, Observer* observer) {
source.AddObserver(observer);
source.RemoveObserver(observer);
},
"The given Source is missing "
"AddObserver(Observer*) and/or RemoveObserver(Observer*) "
"methods. Please provide a custom specialization of "
"ScopedObservationTraits<> for this Source/Observer pair.");
static void AddObserver(Source* source, Observer* observer) {
source->AddObserver(observer);
}
static void RemoveObserver(Source* source, Observer* observer) {
source->RemoveObserver(observer);
}
};
} // namespace base
#endif // BASE_SCOPED_OBSERVATION_TRAITS_H_