Re: DIP 1011--extern(delegate)--Preliminary Review Round 1
On Saturday, 21 July 2018 at 17:54:17 UTC, soolaïman wrote: I know this one year old already but the DIP is still in formal review. [...] This doesn't work because the ABI of a normal function is NOT THE SAME as the ABI of a delegate. That's the only reason the DIP exists is to solve this ABI problem.
Re: DIP 1011--extern(delegate)--Preliminary Review Round 1
I know this one year old already but the DIP is still in formal
review.
I Think the inability to create a delegate with a custom object
as its context similar to delegates created from member functions
should be fixed in a library solution rather than making a
language change. A simple implementation that you could try:
```
import std.traits;
@system ReturnType!F delegate(Parameters!F[1..$])
makeExternDelegate(F)(F fp, void* this_) {
struct Delegate { void* ctxptr; F fptr; }
auto dlg = Delegate(this_, fp);
auto _tmp = cast(void*)
auto dlgp = cast(typeof(return)*) _tmp;
return *dlgp;
}
unittest
{
struct O { int val; }
auto objp = new O(1);
static int getVal(O* this_) {return this_.val;}
auto dlg = makeExternDelegate(, objp);
dlg();
assert(dlg() == 1);
objp.val = 1123;
assert(dlg() != 1);
assert(dlg() == 1123);
}
```
However I think the compiler should still disambiguate the output
of the addressof (&) operator between free and member functions,
I find the difference to be rather an implementation detail that
a user should not have to worry about. I also find this DIP to be
like an awkward deprecation process for such disambiguation.
Perhaps this should rather be on the list of breaking changes of
D3. D3 would be where the language would grow up from past
mistakes, even if that should break compatibility with C! I know,
no body cares about that.
Re: DIP 1011--extern(delegate)--Preliminary Review Round 1
On Monday, 24 July 2017 at 15:27:10 UTC, Steven Schveighoffer wrote: I don't like it so much but also something like this could be considered: out!(x => x>0) or out!x(x > 0) that can't collide with current syntax I think you meant this for DIP 1009? -Steve You're right, I had too many windows opened :) Andrea
Re: DIP 1011--extern(delegate)--Preliminary Review Round 1
On 7/24/17 7:08 AM, Andrea Fontana wrote: On Friday, 14 July 2017 at 10:43:05 UTC, Mike Parker wrote: DIP 1011 is titled "extern(delegate)". https://github.com/dlang/DIPs/blob/master/DIPs/DIP1011.md All review-related feedback on and discussion of the DIP should occur in this thread. The review period will end at 11:59 PM ET on July 28 (3:59 AM GMT July 29), or when I make a post declaring it complete. At the end of Round 1, if further review is deemed necessary, the DIP will be scheduled for another round. Otherwise, it will be queued for the formal review and evaluation by the language authors. Thanks in advance to all who participate. Destroy! I don't like it so much but also something like this could be considered: out!(x => x>0) or out!x(x > 0) that can't collide with current syntax I think you meant this for DIP 1009? -Steve
Re: DIP 1011--extern(delegate)--Preliminary Review Round 1
On Monday, 17 July 2017 at 15:16:45 UTC, Jonathan Marler wrote: On Sunday, 16 July 2017 at 11:45:09 UTC, Nicholas Wilson wrote: [...] I don't see any relation. Looks like the lambda capture lowers to defining a temporary struct and assigning the captured values to fields in that struct, then the lambda is defined as a member function of that struct. That member function already uses the delegate ABI where the context is a reference to the temporary struct. [...] Fair enough.
Re: DIP 1011--extern(delegate)--Preliminary Review Round 1
On Friday, 14 July 2017 at 10:43:05 UTC, Mike Parker wrote: DIP 1011 is titled "extern(delegate)". https://github.com/dlang/DIPs/blob/master/DIPs/DIP1011.md All review-related feedback on and discussion of the DIP should occur in this thread. The review period will end at 11:59 PM ET on July 28 (3:59 AM GMT July 29), or when I make a post declaring it complete. At the end of Round 1, if further review is deemed necessary, the DIP will be scheduled for another round. Otherwise, it will be queued for the formal review and evaluation by the language authors. Thanks in advance to all who participate. Destroy! I don't like it so much but also something like this could be considered: out!(x => x>0) or out!x(x > 0) that can't collide with current syntax
Re: DIP 1011--extern(delegate)--Preliminary Review Round 1
On Sunday, 16 July 2017 at 11:45:09 UTC, Nicholas Wilson wrote:
On Friday, 14 July 2017 at 10:43:05 UTC, Mike Parker wrote:
DIP 1011 is titled "extern(delegate)".
https://github.com/dlang/DIPs/blob/master/DIPs/DIP1011.md
All review-related feedback on and discussion of the DIP
should occur in this thread. The review period will end at
11:59 PM ET on July 28 (3:59 AM GMT July 29), or when I make a
post declaring it complete.
At the end of Round 1, if further review is deemed necessary,
the DIP will be scheduled for another round. Otherwise, it
will be queued for the formal review and evaluation by the
language authors.
Thanks in advance to all who participate.
Destroy!
Not that it is a requirement to consider fir this DIP, but how
would this play with Vittorio's lambda Value capture DIP(?)?
I don't see any relation. Looks like the lambda capture lowers
to defining a temporary struct and assigning the captured values
to fields in that struct, then the lambda is defined as a member
function of that struct. That member function already uses the
delegate ABI where the context is a reference to the temporary
struct.
void main()
{
int x;
string s;
auto dg = [x,s]() => {
// ...
}
/*
lowers to something like this
struct __lambda_struct__
{
int x;
string s;
// This method already has a context, cannot make it
extern(delegate)
void execute()
{
// ...
}
}
auto dg = &__lambda_struct__(x, s).execute;
*/
}
Re: DIP 1011--extern(delegate)--Preliminary Review Round 1
On Friday, 14 July 2017 at 10:43:05 UTC, Mike Parker wrote: DIP 1011 is titled "extern(delegate)". https://github.com/dlang/DIPs/blob/master/DIPs/DIP1011.md All review-related feedback on and discussion of the DIP should occur in this thread. The review period will end at 11:59 PM ET on July 28 (3:59 AM GMT July 29), or when I make a post declaring it complete. At the end of Round 1, if further review is deemed necessary, the DIP will be scheduled for another round. Otherwise, it will be queued for the formal review and evaluation by the language authors. Thanks in advance to all who participate. Destroy! Not that it is a requirement to consider fir this DIP, but how would this play with Vittorio's lambda Value capture DIP(?)?
Re: DIP 1011--extern(delegate)--Preliminary Review Round 1
On Friday, 14 July 2017 at 17:02:37 UTC, Dmitry Olshansky wrote: ...The dance with making an ABI wrapper can be left to compiler proper. This proposal doesn't make ABI wrappers, it changes the ABI of the function itself.
Re: DIP 1011--extern(delegate)--Preliminary Review Round 1
On 7/14/17 1:18 PM, Jonathan Marler wrote:
On Friday, 14 July 2017 at 12:52:56 UTC, Steven Schveighoffer wrote:
On 7/14/17 6:43 AM, Mike Parker wrote:
DIP 1011 is titled "extern(delegate)".
https://github.com/dlang/DIPs/blob/master/DIPs/DIP1011.md
All review-related feedback on and discussion of the DIP should occur
in this thread. The review period will end at 11:59 PM ET on July 28
(3:59 AM GMT July 29), or when I make a post declaring it complete.
At the end of Round 1, if further review is deemed necessary, the DIP
will be scheduled for another round. Otherwise, it will be queued for
the formal review and evaluation by the language authors.
Thanks in advance to all who participate.
Destroy!
It seems reasonable.
One concern I have is this:
extern(delegate) ref int foo(ref int x) { return x; }
int x;
auto dg = // is dg an int * or a delegate?
Currently, this means the former. I'm concerned about ambiguities and
how to resolve them if all of a sudden someone decides it's a good
idea to change their functions to extern(delegate), and code like this
silently switches over. Or someone tries to form a delegate from one
of these, but instead ends up calling the function instead.
I thought about this use case and it's an interesting one.
TLDR; it should return "int delegate()" not "int*"
I can say from experience, this can wreak havoc on things like template
constraints. Changing behavior subtly for the same syntax has consequences.
I wonder if there should be a deprecation period. It's an odd case,
because it only happens if the declaration is changed to
extern(delegate), which means before the change would be introduced, no
code would break.
But I fully see quite a few people doing this because people write a lot
of UFCS functions these days, and slapping an extern(delegate): label
for these functions might be just the blunt instrument people reach for.
I also see people doing without realizing it's not
going to create a delegate. It may be obvious to the compiler that it's
wrong, so they may still get an error. Where I see possible problems is
things like template constraints (e.g. if(is(typeof() == int *)) )
However, we do have precedent that is different for @property
functions vs. normal ones, so there is some validity to your chosen
path. And the opposite choice (int *) would make it impossible to take a
delegate to such a function.
-Steve
Re: DIP 1011--extern(delegate)--Preliminary Review Round 1
On Friday, 14 July 2017 at 12:52:56 UTC, Steven Schveighoffer
wrote:
On 7/14/17 6:43 AM, Mike Parker wrote:
DIP 1011 is titled "extern(delegate)".
https://github.com/dlang/DIPs/blob/master/DIPs/DIP1011.md
All review-related feedback on and discussion of the DIP
should occur in this thread. The review period will end at
11:59 PM ET on July 28 (3:59 AM GMT July 29), or when I make a
post declaring it complete.
At the end of Round 1, if further review is deemed necessary,
the DIP will be scheduled for another round. Otherwise, it
will be queued for the formal review and evaluation by the
language authors.
Thanks in advance to all who participate.
Destroy!
It seems reasonable.
One concern I have is this:
extern(delegate) ref int foo(ref int x) { return x; }
int x;
auto dg = // is dg an int * or a delegate?
Currently, this means the former. I'm concerned about
ambiguities and how to resolve them if all of a sudden someone
decides it's a good idea to change their functions to
extern(delegate), and code like this silently switches over. Or
someone tries to form a delegate from one of these, but instead
ends up calling the function instead.
-Steve
I thought about this use case and it's an interesting one.
TLDR; it should return "int delegate()" not "int*"
First I want to say this use case happens less often then you
might think. It's only a problem when the function has no
arguments. If the function does have arguments then omitting the
parameter list clearly means the application wants a
delegate/function pointer. Currently, taking the address of a
member function call will return a delegate, even if it returns a
reference.
import std.stdio;
struct Foo
{
static int staticInt;
ref int bar()
{
return staticInt;
}
}
Foo foo;
writeln(typeid()); // prints "int delegate()"
// NOTE: If you want to take the address of the return value, you
add the () to the call, i.e.
writeln(typeid(())); // prints "int*"
Furthermore, since taking the address of a UFCS call currently
has no meaning, this would evaluate to int* if it was a UFCS call:
ref int baz(ref Foo foo)
{
static int staticInt;
return staticInt;
}
writeln(typeid()); // prints "int*"
So the semantic analyzer has a precendence for the '&' operator
when applied to "dotted" function calls. It checks if the
expression could result in a delegate, if not then it falls back
to taking the address of the return value.
As you have noticed, since extern(delegate) adds meaning to
taking the address of a UFCS call, the semantic analyzer will now
be able to create a delegate in a place where it previously
couldn't.
extern(delegate) ref int baz(ref Foo foo)
{
static int staticInt;
return staticInt;
}
writeln(typeid()); // is it "int*" or "int delegate()"?
The implementation could go either way but I think it should be
consistent with the semantics for delegates meaning it should
result in "int delegate()" and here's why:
* Having an inconsistent precedence for member functions and
extern(delegate) functions would be confusing
* If taking the address of the return value has precendence, we
would have to come up with a new syntax when the application
wants to do the opposite. Currently, if the application really
means they want to take the address of the return value, they can
simply add an empty parameter list to disambiguate the meaning,
i.e. they could use () instead of If we used
the opposite precedence, there is currently no way to say we
really want a delegate instead of taking the address of the
return value.
* If an existing project does start using extern(delegate), in
almost all cases the change from taking the address of the return
value to getting a delegate will almost always result in a
compile time error. In your example if the meaning of
changed, it would return a different type which would very likely
be caught by the compiler, depending of course on how the value
is used. There are cases where it wouldn't be caught, but it's
very unlikely.
* This only affects code that goes back and modifies their
application to use extern(delegate). In other words, it's not
breaking existing code unless that existing code itself changes
to use this feature.
Re: DIP 1011--extern(delegate)--Preliminary Review Round 1
On 7/14/17 1:02 PM, Dmitry Olshansky wrote: On Friday, 14 July 2017 at 10:43:05 UTC, Mike Parker wrote: DIP 1011 is titled "extern(delegate)". https://github.com/dlang/DIPs/blob/master/DIPs/DIP1011.md Contrary to other poster I believe this is wrong way to solve a problem. A far simpler approach is to allow compiler implicitly convert function pointer to delegate. The dance with making an ABI wrapper can be left to compiler proper. And no annotation hell. But I think the idea is to avoid the extra indirection and call, no? We already have toDelegate, which works fine if you don't care about that. -Steve
Re: DIP 1011--extern(delegate)--Preliminary Review Round 1
On Friday, 14 July 2017 at 10:43:05 UTC, Mike Parker wrote: DIP 1011 is titled "extern(delegate)". https://github.com/dlang/DIPs/blob/master/DIPs/DIP1011.md Contrary to other poster I believe this is wrong way to solve a problem. A far simpler approach is to allow compiler implicitly convert function pointer to delegate. The dance with making an ABI wrapper can be left to compiler proper. And no annotation hell. --- Dmitry Olshansky
Re: DIP 1011--extern(delegate)--Preliminary Review Round 1
On Friday, 14 July 2017 at 10:43:05 UTC, Mike Parker wrote: DIP 1011 is titled "extern(delegate)". Looks good!
Re: DIP 1011--extern(delegate)--Preliminary Review Round 1
On 7/14/17 6:43 AM, Mike Parker wrote:
DIP 1011 is titled "extern(delegate)".
https://github.com/dlang/DIPs/blob/master/DIPs/DIP1011.md
All review-related feedback on and discussion of the DIP should occur in
this thread. The review period will end at 11:59 PM ET on July 28 (3:59
AM GMT July 29), or when I make a post declaring it complete.
At the end of Round 1, if further review is deemed necessary, the DIP
will be scheduled for another round. Otherwise, it will be queued for
the formal review and evaluation by the language authors.
Thanks in advance to all who participate.
Destroy!
It seems reasonable.
One concern I have is this:
extern(delegate) ref int foo(ref int x) { return x; }
int x;
auto dg = // is dg an int * or a delegate?
Currently, this means the former. I'm concerned about ambiguities and
how to resolve them if all of a sudden someone decides it's a good idea
to change their functions to extern(delegate), and code like this
silently switches over. Or someone tries to form a delegate from one of
these, but instead ends up calling the function instead.
-Steve
Re: DIP 1011--extern(delegate)--Preliminary Review Round 1
On Friday, 14 July 2017 at 10:43:05 UTC, Mike Parker wrote: DIP 1011 is titled "extern(delegate)". Looks good to me, useful, doesn't brake code, DIP seems correct.
DIP 1011--extern(delegate)--Preliminary Review Round 1 Begins
The first preliminary review round of DIP 1011, "extern(delegate)", has begun. http://forum.dlang.org/thread/topmfucguenqpucsb...@forum.dlang.org
DIP 1011--extern(delegate)--Preliminary Review Round 1
DIP 1011 is titled "extern(delegate)". https://github.com/dlang/DIPs/blob/master/DIPs/DIP1011.md All review-related feedback on and discussion of the DIP should occur in this thread. The review period will end at 11:59 PM ET on July 28 (3:59 AM GMT July 29), or when I make a post declaring it complete. At the end of Round 1, if further review is deemed necessary, the DIP will be scheduled for another round. Otherwise, it will be queued for the formal review and evaluation by the language authors. Thanks in advance to all who participate. Destroy!
