http://d.puremagic.com/issues/show_bug.cgi?id=2753

           Summary: Cannot declare pointer to function returning ref
           Product: D
           Version: 2.025
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: bugzilla@digitalmars.com
        ReportedBy: jlquinn@optonline.net


ref int c() { static int a=2; return a; }
ref int function() d = &c; // line 8

foo.d(8): variable foo.d only parameters or foreach declarations can be ref

Type inference, however, is able to figure it out:

ref int c() { static int a=2; return a; }
auto d = &c; // whee

Correctly reporting the issue from bug 2735


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http://d.puremagic.com/issues/show_bug.cgi?id=2753


smjg@iname.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |smjg@iname.com
           Keywords|                            |spec




------- Comment #1 from smjg@iname.com  2009-03-21 17:34 -------
The problem seems to be an ambiguity in the grammar: is it ref (int function())
or (ref int) function()?

Maybe we need a bracket notation for ref like we have for const and invariant.

Note that, if we have both this and the notation proposed in bug 1961, ref and inout would no longer be synonyms.


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http://d.puremagic.com/issues/show_bug.cgi?id=2753





------- Comment #2 from maxmo@pochta.ru  2009-03-22 03:00 -------
judging from compiler error messages, ref is not a type modifier, it's a function attribute, so brackets won't help. It should also be noted, that others function attributes' grammar is also ambiguous.
---
nothrow int function() foo();
---
What is nothrow here?

---
const int foo();
---
What is const here?

---
int foo(ref int function() goo);
---
This one would probably give no error.

Is it keyword saving issue? Semantically different things have the same syntax.
If Walter wants context-dependent keywords, he should mark those contexts
better.
I would like to see function attributes at predictable, easy-to-spot locations,
so it would be no chanse to mess storage class with function attributes. There
are already good places for function attributes (after function) and storage
class attributes (before type). If the attributes will be restricted to
corresponding places, there will be no ambiguity (except const).
---
int foo(ref int function() goo); //ref parameter
int goo(int function() ref foo); //return byref function
---


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http://d.puremagic.com/issues/show_bug.cgi?id=2753





------- Comment #3 from smjg@iname.com  2009-03-22 16:50 -------
(In reply to comment #2)
> judging from compiler error messages, ref is not a type modifier, it's a function attribute, so brackets won't help.

I'm a little confused - if that were the case, surely it would work?

Moreover, what is there preventing ref from becoming a type modifier, if this would fix the problem?

It should also be noted, that
> others function attributes' grammar is also ambiguous.
> ---
> nothrow int function() foo();
> ---
> What is nothrow here?

So there's actually an advantage to the suffix notation for function attributes.

> ---
> const int foo();
> ---
> What is const here?
> 
> ---
> int foo(ref int function() goo);
> ---
> This one would probably give no error.

But that is a case that really is ambiguous.

> Is it keyword saving issue? Semantically different things have the same syntax.
> If Walter wants context-dependent keywords, he should mark those contexts
> better.
> I would like to see function attributes at predictable, easy-to-spot locations,
> so it would be no chanse to mess storage class with function attributes. There
> are already good places for function attributes (after function) and storage
> class attributes (before type). If the attributes will be restricted to
> corresponding places, there will be no ambiguity (except const).
> ---
> int foo(ref int function() goo); //ref parameter
> int goo(int function() ref foo); //return byref function
> ---

I don't really like this.  The ref essentially means the same thing, it's just whether it applies to the parameter or the return.  In the latter, it's being moved further from what it applies to: the return type.

IIRC, the equivalent C++ syntax is

int foo(int (*&goo)());  // ref parameter
int goo(int& (*foo)());  // ref return in parameter

It isn't exactly clear, but at least it's unambiguous.  If D got the & notation for reference, we would have

int foo(int function()& goo);  // ref parameter
int goo(int& function() foo);  // ref return in parameter

Indeed, we could have ref take the place of & in this notation

int foo(int function() ref goo);  // ref parameter
int goo(int ref function() foo);  // ref return in parameter

and so the syntax of ref/& would become consistent with that of *.

We could do it like this, or we could make ref a type modifier along the lines of const.  Take your pick.


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http://d.puremagic.com/issues/show_bug.cgi?id=2753





------- Comment #4 from maxmo@pochta.ru  2009-03-24 04:17 -------
(In reply to comment #3)
> int foo(int function() ref goo);  // ref parameter
> int goo(int ref function() foo);  // ref return in parameter
Providing the place between return type and function name for function attributes... interesting...


-- 

http://d.puremagic.com/issues/show_bug.cgi?id=2753





------- Comment #5 from smjg@iname.com  2009-03-24 04:26 -------
(In reply to comment #4)
> (In reply to comment #3)
>> int foo(int function() ref goo);  // ref parameter
>> int goo(int ref function() foo);  // ref return in parameter
> Providing the place between return type and function name for function attributes... interesting...

Any particular reason you feel it still has to count as a function attribute?


-- 

http://d.puremagic.com/issues/show_bug.cgi?id=2753





------- Comment #6 from maxmo@pochta.ru  2009-03-26 03:46 -------
1) if it can why not?
2) this is usable for other function attributes


-- 

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yebblies <yebblies@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |eatingstaples@gmail.com


--- Comment #7 from yebblies <yebblies@gmail.com> 2011-06-06 19:46:53 PDT ---
*** Issue 5421 has been marked as a duplicate of this issue. ***

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yebblies <yebblies@gmail.com> changed:

           What    |Removed                     |Added
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                 CC|                            |timon.gehr@gmx.ch


--- Comment #8 from yebblies <yebblies@gmail.com> 2011-06-06 21:26:33 PDT ---
*** Issue 5828 has been marked as a duplicate of this issue. ***

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Walter Bright <bugzilla@digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bugzilla@digitalmars.com
           Severity|normal                      |enhancement


--- Comment #9 from Walter Bright <bugzilla@digitalmars.com> 2012-01-23 00:34:00 PST ---
ref is a storage class - not a function attribute or type modifier. The grammar isn't broken, it's just a quirk in it. Changing it would be an enhancement request.

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