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March 01, 2011 Template argument deduction | ||||
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I have... import std.stdio; int main(string[] args) { foo([[1,2],[3,4],[5,6]]); // ERROR [1] bar([[1,2],[3,4],[5,6]]); // OK foo!int([[1,2],[3,4],[5,6]]); // OK return 0; } void foo(T)(T[2][] t) { writeln(typeid(t)); } void bar(T)(T[][] t) { writeln(typeid(t)); } [1] src\main.d(4): Error: template main.foo(T) does not match any function template declaration src\main.d(4): Error: template main.foo(T) cannot deduce template function from argument types !()(int[][]) Why can't compiler deduce template parameters from arguments in the first instantiation? Thanks in advance, Tom; |
March 01, 2011 Re: Template argument deduction | ||||
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Posted in reply to Tom | On 02/28/2011 07:39 PM, Tom wrote: > I have... > > import std.stdio; > > int main(string[] args) { > foo([[1,2],[3,4],[5,6]]); // ERROR [1] > bar([[1,2],[3,4],[5,6]]); // OK > foo!int([[1,2],[3,4],[5,6]]); // OK > > return 0; > } > > void foo(T)(T[2][] t) { > writeln(typeid(t)); > } > > void bar(T)(T[][] t) { > writeln(typeid(t)); > } > > [1] > src\main.d(4): Error: template main.foo(T) does not match any function > template declaration > src\main.d(4): Error: template main.foo(T) cannot deduce template > function from argument types !()(int[][]) > > > Why can't compiler deduce template parameters from arguments in the > first instantiation? > > Thanks in advance, > Tom; That's because the type of literals like [1, 2] are slices (dynamic arrays), not fixed-sized arrays. import std.stdio; void main() { writeln(typeof([1,2]).stringof); } The output of that program is int[] Ali |
March 01, 2011 Re: Template argument deduction | ||||
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Posted in reply to Ali Çehreli | Ali Çehreli:
> That's because the type of literals like [1, 2] are slices (dynamic arrays), not fixed-sized arrays.
Then why is this accepted?
foo!int([[1,2],[3,4],[5,6]]); // OK
Bye,
bearophile
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March 01, 2011 Re: Template argument deduction | ||||
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Posted in reply to bearophile | On 02/28/2011 07:39 PM, Tom wrote: > foo([[1,2],[3,4],[5,6]]); // ERROR [1] > bar([[1,2],[3,4],[5,6]]); // OK > foo!int([[1,2],[3,4],[5,6]]); // OK ... > void foo(T)(T[2][] t) { > writeln(typeid(t)); > } > > void bar(T)(T[][] t) { > writeln(typeid(t)); > } On 03/01/2011 04:30 AM, bearophile wrote: > Ali Çehreli: > >> That's because the type of literals like [1, 2] are slices (dynamic >> arrays), not fixed-sized arrays. > > Then why is this accepted? > > foo!int([[1,2],[3,4],[5,6]]); // OK If I have to guess, I think supplying T as int now becomes a problem of matching [1,2] with int[2] and it already works: int[2] a = [1, 2]; int[2][] b = [ [1, 2] ]; I don't know whether the compiler should go the extra mile and help Tom in the original case. :-/ Ali |
March 02, 2011 Re: Template argument deduction | ||||
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Posted in reply to Ali Çehreli | El 01/03/2011 16:05, Ali Çehreli escribió:
> On 02/28/2011 07:39 PM, Tom wrote:
>
> > foo([[1,2],[3,4],[5,6]]); // ERROR [1]
> > bar([[1,2],[3,4],[5,6]]); // OK
> > foo!int([[1,2],[3,4],[5,6]]); // OK
>
> ...
>
> > void foo(T)(T[2][] t) {
> > writeln(typeid(t));
> > }
> >
> > void bar(T)(T[][] t) {
> > writeln(typeid(t));
> > }
>
> On 03/01/2011 04:30 AM, bearophile wrote:
>
> > Ali Çehreli:
> >
> >> That's because the type of literals like [1, 2] are slices (dynamic
> >> arrays), not fixed-sized arrays.
> >
> > Then why is this accepted?
> >
> > foo!int([[1,2],[3,4],[5,6]]); // OK
>
> If I have to guess, I think supplying T as int now becomes a problem of
> matching [1,2] with int[2] and it already works:
>
> int[2] a = [1, 2];
> int[2][] b = [ [1, 2] ];
>
> I don't know whether the compiler should go the extra mile and help Tom
> in the original case. :-/
>
> Ali
>
I should post on D newsgroup. Perhaps Walter or Andrei could enlight us about this.
Thanks,
Tom;
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