• Andre Pany (15/15) Aug 03 2016 Hi,
• Anonymouse (12/33) Aug 03 2016 ...is an alias for a delegate/function returning an Object. It is
• Andre Pany (6/26) Aug 03 2016 Thanks for the info. Yes, I forgot the () for new Object;
• ag0aep6g (2/4) Aug 04 2016 `new Object` without parentheses is perfectly fine.
• Kagamin (2/2) Aug 04 2016 Function pointers and delegates are not intended to allow

Andre Pany <andre s-e-a-p.de> writes:

Hi,

I just stumbled over this behavior. I am not sure whether
the behavior is correct or not.

alias foo = () => new Object;
void bar(Object o){}

void main()
{
	auto n1 = foo;
	bar(foo);
}

While first line in main is working fine,
second line does not compile due to missing ().

Is this correct?

Kind regards
André

Anonymouse <asdf asdf.net> writes:

On Wednesday, 3 August 2016 at 17:16:10 UTC, Andre Pany wrote:
 Hi,

 I just stumbled over this behavior. I am not sure whether
 the behavior is correct or not.
 [...]

 alias foo = () => new Object;

...is an alias for a delegate/function returning an Object. It is 
analogous to
 alias foo = () { return new Object; };

 void bar(Object o){}

...is a function accepting an Object parameter. In main you are 
trying to call this overload
 void bar(Object function() o){}

...which is essentially
 void bar(typeof(foo) o) {}

You can use pragma(msg, typeof(symbol).stringof) to inspect what 
types are being thrown around.
 void bar(T)(T t)
 {
     pragma(msg, T.stringof); // "Object function() pure nothrow 
  safe"
 }

 void main()
 {
     auto n1 = foo;
     pragma(msg, typeof(foo).stringof); // "Object function() 
 pure nothrow  safe"
     bar(foo);
 }

You could argue that parameterless function call rules should 
apply here and have it implicitly converted to bar(foo()), but it 
doesn't. I imagine the ambiguity (of delegate vs function return 
value) would just cause more problems than it would solve.

Andre Pany <andre s-e-a-p.de> writes:

On Wednesday, 3 August 2016 at 18:15:23 UTC, Anonymouse wrote:
 On Wednesday, 3 August 2016 at 17:16:10 UTC, Andre Pany wrote:
 [...]

 [...]

 ...is an alias for a delegate/function returning an Object. It 
 is analogous to
 [...]

 [...]

 ...is a function accepting an Object parameter. In main you are 
 trying to call this overload
 [...]

 ...which is essentially
 [...]

 You can use pragma(msg, typeof(symbol).stringof) to inspect 
 what types are being thrown around.
 [...]

 You could argue that parameterless function call rules should 
 apply here and have it implicitly converted to bar(foo()), but 
 it doesn't. I imagine the ambiguity (of delegate vs function 
 return value) would just cause more problems than it would 
 solve.

Thanks for the info. Yes, I forgot the () for new Object;
Adding the () for new Object() still returns the same error.
I think you are right with the ambiguity.

Kind regards
André

ag0aep6g <anonymous example.com> writes:

On 08/03/2016 09:40 PM, Andre Pany wrote:
 Thanks for the info. Yes, I forgot the () for new Object;
 Adding the () for new Object() still returns the same error.

`new Object` without parentheses is perfectly fine.

Kagamin <spam here.lot> writes:

Function pointers and delegates are not intended to allow 
optional parentheses. See also DIP23.