Thread overview | |||||
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June 03, 2012 alias this with template class? | ||||
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I think this should work: [code] import std.stdio; class Foo(T) { public: T Num; @property Foo!(U) ConvertTo(U)() inout { return cast(Foo!(U)) this; } alias ConvertTo this; } void Call(const Foo!(float) FFoo) { } void main() { Foo!(ubyte) UbFoo = new Foo!(ubyte)(); Call(UbFoo); readln(); } [/code] Why it doesn't? |
June 03, 2012 Re: alias this with template class? | ||||
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Posted in reply to Namespace | On 06/03/2012 08:43 PM, Namespace wrote:
> I think this should work:
>
> [code]
> import std.stdio;
>
> class Foo(T) {
> public:
> T Num;
>
> @property
> Foo!(U) ConvertTo(U)() inout {
> return cast(Foo!(U)) this;
> }
>
> alias ConvertTo this;
> }
>
> void Call(const Foo!(float) FFoo) {
>
> }
>
> void main() {
> Foo!(ubyte) UbFoo = new Foo!(ubyte)();
>
> Call(UbFoo);
>
> readln();
> }
> [/code]
>
> Why it doesn't?
Making this generally work as you expect would be too hard.
The compiler would have to reverse-engineer the 'ConvertTo' template
which is an undecidable problem in general. Some clever heuristics
might suffice for most practical instances though, but those are
very open-ended and therefore it is hard to incorporate them into the
language definition. If you think it should be done you could file a
suggestion (enhancement request) into the bug tracker.
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June 03, 2012 Re: alias this with template class? | ||||
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Posted in reply to Timon Gehr | Fail. Ok, i tried something like this: [code] import std.stdio; mixin template TConvertTo(T : Object, U) { T!(U) ConvertTo() inout { return cast(T!U) this; } alias ConvertTo this; } class Foo(T) { public: T Num; mixin TConvertTo!(typeof(this), float); } [/code] but it fails with: template_alias_this_cast.d(4): Error: template instance T!(float) T is not a template declaration, it is a class template_alias_this_cast.d(4): Error: T!(float) is used as a type template_alias_this_cast.d(15): Error: mixin template_alias_this_cast.Foo!(float).Foo.TConvertTo!(Foo,float) error instantiating template_alias_this_cast.d(19): Error: template instance template_alias_this_cast.Foo!(float) error instantiating If i change it to: [code] import std.stdio; mixin template TConvertTo(V) { Foo!(V) ConvertTo() inout { return cast(Foo!V) this; } alias ConvertTo this; } class Foo(T) { public: T Num; mixin TConvertTo!(float); } [/code] it works. But i think my first idea should work, too. |
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