Parameterized template value parameter

[Yuxuan Shui via Digitalmars-d]

On Friday, 24 March 2017 at 20:43:18 UTC, Dmitry Olshansky wrote:
> On 3/24/17 12:24 AM, Yuxuan Shui wrote:
>> So I was trying to make my template take a value parameter, 
>> whose type
>> is also a parameter to the template. e.g.:
>>
>>     template A(Char[] str, Char);
>>
>> But dmd complains about 'Char' being undefined. I have to 
>> write:
>>
>>     template A(Char, Char[] str);
>>
>> Which is inconvenient, because now 'Char' can't be deduced by 
>> the compiler.
>>
>> Can we make the first case work?
>
> How about this?
>
> template A(alias str)
> if(is(typeof(str) : Char[], Char)){
> 	alias Char = typeof(str[0]);
> //	...
> }

Yes. This is what I ended up doing 
(https://github.com/yshui/sdpc/blob/master/sdpc/parsers.d#L45).

One problem of this is that 'str' is not longer restricted to be 
a compile time value. Which is probably fine, but kind of makes 
me uncomfortable.

>
> In general it's sometimes possible to do the deduction w/o 
> introducing more template arguments.
>
> ---
> Dmitry Olshansky