• "Joshua Niehus" <jm.niehus gmail.com> Feb 27 2012
• "Jesse Phillips" <jessekphillips+D gmail.com> Feb 27 2012
• Timon Gehr <timon.gehr gmx.ch> Feb 27 2012
• "Puming" <zhaopuming gmail.com> Feb 27 2012
• "Joshua Niehus" <jm.niehus gmail.com> Feb 27 2012
• James Miller <james aatch.net> Feb 27 2012
• "Jesse Phillips" <jessekphillips+D gmail.com> Feb 27 2012
• "Jonathan M Davis" <jmdavisProg gmx.com> Feb 28 2012

"Joshua Niehus" <jm.niehus gmail.com> writes:

Hello,

I dont understand the following snippet's output:

import std.stdio, std.traits;
void main() {
     writeln(isSomeFunction!(writeln));
     writeln(isCallable!(writeln));
     writeln("Yes I am...");
}

/* OUTPUT */
false
false
Yes I am...

If 'writeln' isn't a method/function and it's not callable, then 
what is it?

Thanks,
Josh

"Jesse Phillips" <jessekphillips+D gmail.com> writes:

On Tuesday, 28 February 2012 at 05:56:12 UTC, Joshua Niehus wrote:
 Hello,

 I dont understand the following snippet's output:

 import std.stdio, std.traits;
 void main() {
     writeln(isSomeFunction!(writeln));
     writeln(isCallable!(writeln));
     writeln("Yes I am...");
 }

 /* OUTPUT */
 false
 false
 Yes I am...

 If 'writeln' isn't a method/function and it's not callable, 
 then what is it?

 Thanks,
 Josh


It is a template.

Timon Gehr <timon.gehr gmx.ch> writes:

On 02/28/2012 07:27 AM, Joshua Niehus wrote:
 On Tuesday, 28 February 2012 at 06:10:11 UTC, Jesse Phillips wrote:
 It is a template.


 I see, thanks.
 And I bet its not possible to figure out if a template is a "function
 template" or a "class template" etc...


You can trivially test whether the symbol is callable with some specific 
arguments, if that helps:

is(typeof(writeln(arg1,arg2,arg3)))

"Puming" <zhaopuming gmail.com> writes:

 It is a template.


Is a template callable? So what's the isCallable and 
isSomeFunction equivalent for templates?

"Joshua Niehus" <jm.niehus gmail.com> writes:

On Tuesday, 28 February 2012 at 06:10:11 UTC, Jesse Phillips 
wrote:
 It is a template.


I see, thanks.
And I bet its not possible to figure out if a template is a 
"function template" or a "class template" etc...

James Miller <james aatch.net> writes:

On 28 February 2012 19:27, Joshua Niehus <jm.niehus gmail.com> wrote:
 On Tuesday, 28 February 2012 at 06:10:11 UTC, Jesse Phillips wrote:
 It is a template.



 I see, thanks.
 And I bet its not possible to figure out if a template is a "function
 template" or a "class template" etc...


Not really, there might be, but not an obvious one. Its because
templates can hold multiple types of declarations, not just functions
or classes. The "eponymous template" pattern you see normally is not
mandatory.

--
James Miller

"Jesse Phillips" <jessekphillips+D gmail.com> writes:

On Tuesday, 28 February 2012 at 06:26:38 UTC, Puming wrote:
 It is a template.


 Is a template callable? So what's the isCallable and 
 isSomeFunction equivalent for templates?


I suppose it could be considered a bug as it is mostly a 
syntactic request/check. I'd expect

assert(isCallable!(writeln!string))

to be true. But as it is callable without explicit 
instantiation...

"Jonathan M Davis" <jmdavisProg gmx.com> writes:

On Tuesday, February 28, 2012 06:56:10 Joshua Niehus wrote:
 Hello,
 
 I dont understand the following snippet's output:
 
 import std.stdio, std.traits;
 void main() {
 writeln(isSomeFunction!(writeln));
 writeln(isCallable!(writeln));
 writeln("Yes I am...");
 }
 
 /* OUTPUT */
 false
 false
 Yes I am...
 
 If 'writeln' isn't a method/function and it's not callable, then
 what is it?


writeln doesn't even really exist as far as the compiler is concerned until 
it's been instantiated. So, testing writeln isn't going to work. You need to 
either test a specific instantiation (e.g. isSomeFunction!(writeln!string))), 
or you need to just test that particular call works (e.g. 
is(typeof(writeln(arg)))). The second is probably better, since that's 
generally what you really care about - is it compilable with the given set of 
arguments.

- Jonathan M Davis