cef_callback.h File Reference

A callback is similar in concept to a function pointer: it wraps a runnable object such as a function, method, lambda, or even another callback, allowing the runnable object to be invoked later via the callback object. More...

#include <stddef.h>
#include "include/base/cef_bind.h"
#include "include/base/cef_callback_forward.h"
#include "include/base/cef_logging.h"
#include "include/base/internal/cef_callback_internal.h"

Classes
class	base::OnceCallback< R(Args...)>
class	base::RepeatingCallback< R(Args...)>

Namespaces
	base

Detailed Description

A callback is similar in concept to a function pointer: it wraps a runnable object such as a function, method, lambda, or even another callback, allowing the runnable object to be invoked later via the callback object.

Unlike function pointers, callbacks are created with base::BindOnce() or base::BindRepeating() and support partial function application.

A base::OnceCallback may be Run() at most once; a base::RepeatingCallback may be Run() any number of times. |is_null()| is guaranteed to return true for a moved-from callback.

  // The lambda takes two arguments, but the first argument |x| is bound at
  // callback creation.
  base::OnceCallback<int(int)> cb = base::BindOnce([] (int x, int y) {
    return x + y;
  }, 1);
  // Run() only needs the remaining unbound argument |y|.
  printf("1 + 2 = %d\n", std::move(cb).Run(2));  // Prints 3
  printf("cb is null? %s\n",
         cb.is_null() ? "true" : "false");  // Prints true
  std::move(cb).Run(2);  // Crashes since |cb| has already run.

Callbacks also support cancellation. A common use is binding the receiver object as a WeakPtr<T>. If that weak pointer is invalidated, calling Run() will be a no-op. Note that |IsCancelled()| and |is_null()| are distinct: simply cancelling a callback will not also make it null.

See https://chromium.googlesource.com/chromium/src/+/lkgr/docs/callback.md for the full documentation.