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June 12, 2012
Template argument types
Do you know why D templates accept floating point values and even 
arrays of 32 bit dchars:

template Foo(dchar[] s) {
    enum size_t Foo = s.length;
}
void main() {
    pragma(msg, Foo!("hello"d.dup));
}


But they don't accept arrays of ints?


template Foo(int[] s) {
    enum size_t Foo = s.length;
}
void main() {
    enum int[] a = [1, 2, 3];
    pragma(msg, Foo!a);
}


===>
test.d(1): Error: arithmetic/string type expected for 
value-parameter, not int[]


This works, but it's not the same thing:

template Foo(alias s) if (is(typeof(s) == int[])) {
    enum size_t Foo = s.length;
}
void main() {
    enum int[] a = [1, 2, 3];
    pragma(msg, Foo!a);
}

Bye and thank you,
bearophile
June 12, 2012
Re: Template argument types
On 12-06-2012 02:04, bearophile wrote:
> Do you know why D templates accept floating point values and even arrays
> of 32 bit dchars:
>
> template Foo(dchar[] s) {
> enum size_t Foo = s.length;
> }
> void main() {
> pragma(msg, Foo!("hello"d.dup));
> }
>
>
> But they don't accept arrays of ints?
>
>
> template Foo(int[] s) {
> enum size_t Foo = s.length;
> }
> void main() {
> enum int[] a = [1, 2, 3];
> pragma(msg, Foo!a);
> }
>
>
> ===>
> test.d(1): Error: arithmetic/string type expected for value-parameter,
> not int[]
>
>
> This works, but it's not the same thing:
>
> template Foo(alias s) if (is(typeof(s) == int[])) {
> enum size_t Foo = s.length;
> }
> void main() {
> enum int[] a = [1, 2, 3];
> pragma(msg, Foo!a);
> }
>
> Bye and thank you,
> bearophile

My guess is that dchar[] is special-cased in the compiler to allow 
passing strings. I think we should extend this to support arrays of all 
primitive types.

-- 
Alex Rønne Petersen
alex@lycus.org
http://lycus.org
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