Allow base::DoNothing() to handle any argument list.
This changes the form of DoNothing() from a simple no-arg function to a class
that produces callbacks via templated operator(). This allows callers to
replace base::Bind(&base::DoNothing) with base::DoNothing() for a small
boilerplate reduction; more importantly, it allows using DoNothing() to replace
existing no-op functions/lambdas that took more than zero args, and thus had to
be manually declared. This removes dozens of such functions and around 600 LOC
total.
In a few places, DoNothing() can't be used directly, and this change also adds
explicit callback-generating Once<>() and Repeatedly<>() members that will
produce a callback with a specific signature.
BUG=811554
TEST=none
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_mojo;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_vr;master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: I37f87b35c6c079a6a8c03ff18ec3a54e1237f126
Reviewed-on: https://chromium-review.googlesource.com/903416
Commit-Queue: Peter Kasting <[email protected]>
Reviewed-by: Jochen Eisinger <[email protected]>
Reviewed-by: Gabriel Charette <[email protected]>
Cr-Commit-Position: refs/heads/master@{#538953}diff --git a/base/bind_helpers.h b/base/bind_helpers.h
index 07d64aeb..fca3939 100644
--- a/base/bind_helpers.h
+++ b/base/bind_helpers.h
@@ -10,6 +10,7 @@
#include <type_traits>
#include <utility>
+#include "base/bind.h"
#include "base/callback.h"
#include "base/memory/weak_ptr.h"
#include "build/build_config.h"
@@ -19,8 +20,28 @@
namespace base {
-// Useful for creating a Closure that does nothing when called.
-BASE_EXPORT void DoNothing();
+// Creates a callback that does nothing when called.
+class BASE_EXPORT DoNothing {
+ public:
+ template <typename... Args>
+ operator RepeatingCallback<void(Args...)>() const {
+ return Repeatedly<Args...>();
+ }
+ template <typename... Args>
+ operator OnceCallback<void(Args...)>() const {
+ return Once<Args...>();
+ }
+ // Explicit way of specifying a specific callback type when the compiler can't
+ // deduce it.
+ template <typename... Args>
+ static RepeatingCallback<void(Args...)> Repeatedly() {
+ return BindRepeating([](Args... args) {});
+ }
+ template <typename... Args>
+ static OnceCallback<void(Args...)> Once() {
+ return BindOnce([](Args... args) {});
+ }
+};
// Useful for creating a Closure that will delete a pointer when invoked. Only
// use this when necessary. In most cases MessageLoop::DeleteSoon() is a better
