• Yuxuan Shui (8/8) Mar 23 2017 So I was trying to make my template take a value parameter, whose
• Dmitry Olshansky (11/18) Mar 24 2017 How about this?
• Yuxuan Shui (6/32) Mar 24 2017 Yes. This is what I ended up doing
• Nicholas Wilson (5/15) Mar 24 2017 To test wether str is a compile time value just check if you can

Yuxuan Shui <yshuiv7 gmail.com> writes:

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?

Dmitry Olshansky <dmitry.olsh gmail.com> writes:

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

Yuxuan Shui <yshuiv7 gmail.com> writes:

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

Nicholas Wilson <iamthewilsonator hotmail.com> writes:

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;})))