diff options
| -rw-r--r-- | mojo/public/cpp/bindings/callback.h | 19 |
1 files changed, 18 insertions, 1 deletions
diff --git a/mojo/public/cpp/bindings/callback.h b/mojo/public/cpp/bindings/callback.h index 60dea1c..4e9a933 100644 --- a/mojo/public/cpp/bindings/callback.h +++ b/mojo/public/cpp/bindings/callback.h @@ -5,6 +5,7 @@ #ifndef MOJO_PUBLIC_CPP_BINDINGS_CALLBACK_H_ #define MOJO_PUBLIC_CPP_BINDINGS_CALLBACK_H_ +#include <type_traits> #include <utility> #include "base/memory/ref_counted.h" @@ -46,7 +47,23 @@ class Callback<void(Args...)> { // As above, but can take an object that isn't derived from Runnable, so long // as it has a compatible operator() or Run() method. operator() will be // preferred if the type has both. - template <typename Sink> + // + // The std::enable_if is used to disable this constructor if the argument is + // derived from Runnable. This is needed because the compiler will pick this + // constructor instead of the Runnable* one above when the argument is of the + // type of the derived class instead of down casted to a Runnable. i.e: + // class Foo : public Callback::Runnable { + // ... + // }; + // Callback cb(new Foo); + // + // The call site can fix this by using a static_cast to down cast to a + // Runnable*, but that shouldn't be necessary. + template < + typename Sink, + typename std::enable_if<!std::is_base_of< + Runnable, + typename std::remove_pointer<Sink>::type>::value>::type* = nullptr> Callback(const Sink& sink) { using sink_type = typename internal::Conditional< internal::HasCompatibleCallOperator<Sink, Args...>::value, |