[webkit-dev] Does someone know how to fix WTF::Function on Windows

Darin Adler darin at apple.com
Sat Jul 15 09:13:20 PDT 2017

Hi folks.

On Windows, WTF::Function doesn’t quite work right. Code that is something like this:

    void addCallback(WTF::Function<void()>&&);

    void testFunction()
        // ...

    void addTestFunction()

Leads to errors like this:

    error C2664: 'void addCallback(WTF::Function<void (void)> &&)': cannot convert argument 1 from 'void (__cdecl *)(void)' to 'WTF::Function<void (void)> &&'
    note: You cannot bind an lvalue to an rvalue reference

The problem might have something to do with cdecl vs. stdcall functions, but I am not sure that is the problem. It could be some other problem with how WTF::Function is written. Or it might even be a bug in the Visual Studio compiler. Since I don’t have a Windows machine myself, I was trying to use EWS to figure this out but that was slow. Then I tried using http://webcompiler.cloudapp.net but I could not reproduce any error there when I pasted in cut down code; it just compiled fine.

Is there someone who knows how to fix this?

Another way to put this is: We want to take off the explicit WTF::Function conversions in functions like canUseWithReason in SimpleLineLayout.cpp, Page::Page in Page.cpp, and Worker::Worker in Worker.cpp and have it still compile and work on Windows. Other platforms seem to compile fine without the explicit WTF::Function.

— Darin

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