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?

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]);
//	...
}

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

---
Dmitry Olshansky

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

On Friday, 24 March 2017 at 21:13:26 UTC, Yuxuan Shui wrote:
> On Friday, 24 March 2017 at 20:43:18 UTC, Dmitry Olshansky
>>
>> template A(alias str)
>> if(is(typeof(str) : Char[], Char)){
>> 	alias Char = typeof(str[0]);
>> //	...
>> }

> 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.

To test wether str is a compile time value just check if you can use it to assign to an enum
if(is(typeof(str) : Char[], Char) && is(typeof({enum foo = str;})))