On Monday, 24 April 2017 at 19:19:27 UTC, Meta wrote:
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
Yes I'm familiar with C# extension methods and that was my
initial thought. The one advantage I saw with naming the
parameter "this" was that it produces more "refactorable" code.
If the first parameter of a delegateable function is a reference
to a struct or a class, then you could move the function inside
the struct/class, take out the first parameter and the code will
work as a member function with no changes since the "this"
keyword will be referring to the same object in both cases. But
it's not a big deal, either syntax works fine in my opinion.
