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digitalmars.D.learn - is(T == const) for function types

reply "mist" <none none.none> writes:
http://dpaste.dzfl.pl/0cda8d0f

bug or feature?
Dec 25 2012
parent reply =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 12/25/2012 12:59 PM, mist wrote:

 http://dpaste.dzfl.pl/0cda8d0f

 bug or feature?


For convenience to others, here is your code:

struct Test
{
     void delegate() const deleg;
}

void main()
{
     static assert( is(typeof(Test.deleg) == const) );
}

I don't know the answer but this works:

struct Test
{
     alias void delegate() Deleg;
     const Deleg deleg;
}

void main()
{
     static assert( is(typeof(Test.deleg) == const) );
}

Ali
Dec 25 2012
parent reply "bearophile" <bearophileHUGS lycos.com> writes:
Ali Çehreli:


 I don't know the answer but this works:


That difference smells of compiler bug :-)

Bye,
bearophile
Dec 25 2012
parent reply =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 12/25/2012 04:13 PM, bearophile wrote:

 Ali Çehreli:


 I don't know the answer but this works:


 That difference smells of compiler bug :-)

 Bye,
 bearophile


Hmmm. I think the compiler is right. That const that is applied "at the 
end" in that syntax is I think allowed only for member functions. 
Otherwise these two work as well:

     // These work:
     const(void delegate()) deleg;
     const void delegate() deleg;

     // This is a compilation error:
     void delegate() const deleg;


Ali
Dec 25 2012
next sibling parent "bearophile" <bearophileHUGS lycos.com> writes:
Ali Çehreli:


 Hmmm. I think the compiler is right. That const that is applied 
 "at the end" in that syntax is I think allowed only for member 
 functions. Otherwise these two work as well:


You seem right. The positional syntax of those tags tricks me 
sometimes still.

Bye,
bearophile
Dec 25 2012
prev sibling parent "mist" <none none.none> writes:
On Wednesday, 26 December 2012 at 00:47:28 UTC, Ali Çehreli wrote:

 On 12/25/2012 04:13 PM, bearophile wrote:

 Ali Çehreli:


 I don't know the answer but this works:


 That difference smells of compiler bug :-)

 Bye,
 bearophilee


 Hmmm. I think the compiler is right. That const that is applied 
 "at the end" in that syntax is I think allowed only for member 
 functions. Otherwise these two work as well:

     // These work:
     const(void delegate()) deleg;
     const void delegate() deleg;

     // This is a compilation error:
     void delegate() const deleg;


 Ali


Yes, looks like I was not checking 
http://dlang.org/declaration.html good enough and assumed C-like 
model where "Type const var" is as legal as "const Type var". 
There is a surprising revelation provided by Kenji in context of 
member variable delegates:

struct Test
{
	void delegate() const deleg;
}

void main()
{
	static if (is(typeof(Test.deleg) F == delegate))
	{
		pragma(msg, "Sure, delegate");
		static assert( is(F == const) );
	}
}

"Delegate type qualifier cannot test directly. You should extract 
function type from it, then test const." (c) Kenji

Copying it here from github for any possible lucky googlers :)
Dec 26 2012