Distinguishing between const and non-const variable in a template?

[Deewiant]

renoX wrote:
> mario pernici a écrit :
>> renoX Wrote:
>>
>>> Hello,
>>>
>>> I'm trying to improve format string by allowing the format
>>> " ... %{x} ...", my problem is that when I give a non-const char[]
>>> parameter in
>>> mixin(Putf!(foo));
>>>
>>> then the template fail..
>>>
>>> How can I reliably detect in a template if the parameter is a
>>> constant or not?
> [cut]
>>
>> Maybe you can use something like this
>>
>>   const char[] s = "ab";
>>   static if(is(typeof(&s))) {
>>     writefln(s, " not constant");
>>   }
>>   else {
>>     static if(is(typeof(s))) {
>>       writefln(s, " constant");
>>     }
>>   }
> 
> Very nice, thanks!
> 
> I'm curious: how did you find this??
> I don't recall seeing it in the documentation and it looks kind of
> magical to me..
> 
> Thanks again,
> renoX
> 

He probably just figured it out: you can't take the address of a constant, so
is(typeof(&s)) is false if s is a constant. I'm not sure about the necessity of
the is(typeof(s)) in the else case, though.

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