On Monday, 24 April 2017 at 15:47:14 UTC, Jonathan Marler wrote:
I've added a DIP for this
(https://github.com/dlang/DIPs/pull/61).
At first I first thought that all we needed was to add
semantics to take the address of a UFCS-style call, but after
messing around with your example I realized that delegates are
not ABI-compatible with functions that take the delegate ptr as
the first parameter. You mentioned that the problem was with
the parameter order and that this should work with extern(C)
functions and I think you're right.
The new DIP proposes the addition of "Extension Methods" which
are functions that are ABI-compatible with delegates. You
define an extension method by naming the first parameter "this":
struct Foo
{
void bar(int x)
{
}
}
void baz(ref Foo this, int x)
{
}
Because the first parameter of baz is named this, it is an
"extension method" of Foo which means it is ABI-compatible with
the method bar.
void delegate(int x) dg;
Foo foo;
dg = &foo.bar; // a normal method delegate
dg(42); // calls foo.bar(42)
dg = &foo.baz; // an extension method delegate
dg(42); // calls baz(foo, 42);
dg = &baz; // a "null delegate", unsafe code, funcptr
points to the baz function, but ptr is null
dg(42); // calls baz(null, 42);
One small tweak is that `this` should act as a storage class
instead of the user having to name the parameter `this`. This is
what C# does so we should mimic it to avoid confusion.
https://www.codeproject.com/Tips/709310/Extension-Method-In-Csharp
