Re: opEquals on shared object

[Steven Schveighoffer via Digitalmars-d-learn]

On 6/30/16 8:30 AM, jj75607 wrote:
On Thursday, 30 June 2016 at 12:21:03 UTC, Steven Schveighoffer wrote:
On 6/30/16 6:26 AM, jj75607 wrote:
Hello!
I need to overload opEquals on shared class C

shared class C
{
    override bool opEquals(Object o) { return false; }
}

But compilation fails with the message:
Error: function f700.C.opEquals does not override any function, did you
mean to override 'object.Object.opEquals'?

What am I doing wrong?

Object.opEquals is not marked shared. You can't override a non-shared
method with a shared one.

You need to remove override.

But... unfortunately, this may not work in practice. The opEquals
handling for objects is pretty much screwed unless you have unshared
mutable objects. I think it may work for const objects, but not in a
good way.

-Steve

Thanks!

But what should I do to fix that code?

shared class C
{
    bool opEquals(Object o) { return false; }
}

class A(T)
{
    void f(T a, T b)
    {
        if(a == b)
            writeln("equals");
        else
            writeln("non equals");
    }
}


int main(string[] argv)
{
    auto a1 = new A!int;
    a1.f(1,2);

    auto a2 = new A!(shared(C));
    shared C c = new shared(C);
    a2.f(c,c);


    return 0;
}

It fails with
    Error: none of the overloads of 'opEquals' are callable using
argument types (shared(C), shared(C))

This is an artifact of the object.opEquals entry point function. It 
handles calling your object's opEquals properly.

Try changing C.opEquals to accept a shared(Object).

If that doesn't work, you may be out of luck until the druntime team 
figures this out. Please file an issue if you can't get it to work.

-Steve