Re: Learning delegates
On Sunday, 8 September 2019 at 10:04:57 UTC, Joel wrote:
I'm trying to understand delegates. Is there any good ways I
can get a better understanding of them?
Simple, don't make it harder than it is.
Delegates are basically functions... that is, function
pointers(they point to some function somewhere in space)... BUT
they include a "context". The context a scope.
{ // In some scope
int x;
d = () { writeln(x); };
}
() { writeln(x); };
is the function defined as a lambda(inline).
It accesses a variable outside of it, that is, in the scope...
which is called the context.
d is the delegate, it is a function pointer that holds the
function AND the context pointer.
We can then do
d();
which called/executes the function... the function is called, and
x can be referenced because d stores the context.
If you do not understand functions, then function pointers, you
can't understand delegates.
Re: Learning delegates
On Sunday, 8 September 2019 at 10:04:57 UTC, Joel wrote: I'm trying to understand delegates. Is there any good ways I can get a better understanding of them? I think this chapter should give you some useful information: http://www.ddili.org/ders/d.en/lambda.html
Re: Learning delegates
On Sunday, 8 September 2019 at 10:04:57 UTC, Joel wrote:
I'm trying to understand delegates. Is there any good ways I
can get a better understanding of them?
I am no compiler implementer, so what is below may contain a lot
of inaccuracies and conceptual shortcuts, but here is my view of
delegates in D. I hope this helps.
Delegates are fat function pointers.
D arrays are also fat function pointers: they can be implemented
as a struct with a size_t length and a pointer to the data:
sruct DArray(T) {
size_t length;
T * data;
}
D delegates can be implemented as a pointer to some context data
and a function pointer, something similar to D arrays:
struct DDelegate(Context, Return, Args) {
Context context;
Return function(Args) functionPointer;
}
The context can be:
- a struct value
- a class instance
- some data from a local function frame when the delegate is used
as a closure.
The compiler replaces a call to the delegate in the source code
by a call to the function pointer with the right data for runtime.
Something like:
dg.functionPointer(dg.context, "hello, world");
Re: Learning delegates
On Sunday, 8 September 2019 at 10:04:57 UTC, Joel wrote: I'm trying to understand delegates. Is there any good ways I can get a better understanding of them? I wrote a foreach loop using opApply. A side effect of that was, that after I managed to do this I understood delegates. :-)
Re: Learning delegates
On Sunday, 8 September 2019 at 10:04:57 UTC, Joel wrote: I'm trying to understand delegates. Is there any good ways I can get a better understanding of them? You may want to read this: https://tour.dlang.org/tour/en/basics/delegates
Learning delegates
I'm trying to understand delegates. Is there any good ways I can get a better understanding of them?
