Template arg deduction

Jul 07, 2021

Kevin Bailey

Jul 07, 2021

Ali Çehreli

Jul 07, 2021

Paul Backus

Jul 07, 2021

Tejas

Jul 07, 2021

vit

On 7/7/21 12:14 PM, Kevin Bailey wrote: > fairly simple template argument deduction It's not the simplest but it is still complicated. :) > I guess D can't crack open a type like that? There are other ways of achieving the same thing the simplest of which is probably the following: void func(B)(B f) { } Apparently, there are additional constraints on B, which can be expressed in D with some flexibility, pragmatism, and optimism. Ali

July 07, 2021

Re: Template arg deduction

Posted by Tejas
in reply to Kevin Bailey

Permalink

Tejas

Posted in reply to Kevin Bailey

Permalink

On Wednesday, 7 July 2021 at 19:14:52 UTC, Kevin Bailey wrote:

I'm trying to use some fairly simple template argument deduction, but
maybe I'm not getting the syntax correct. C++ doesn't event blink at
something like this, but D is giving me:

temptest.d(18): Error: template temptest.func cannot deduce function from argument types !()(bar), candidates are:
temptest.d(10): func(T)(foo!T.bar f)

I guess D can't crack open a type like that?

template foo(T)
{
class bar
{
        T t;
}

}

void func(T)(            // 10
        foo!(T).bar f)
{
}

int main()
{
        foo!int.bar fi;
        func(fi);        // 18
}

The following works:
```d
import std.stdio;
template foo(T)
{
class bar
{
        T t;
}

}

void func(T) (            // 10
        T f)               //  No need to repeat foo!(int).bar :)
{
}

int main()
{
        foo!(int).bar fi;//brackets added, now syntax is correct
        func(fi);        // 18. int couldn't get deduced here
    return 0;
}
```

On Wednesday, 7 July 2021 at 19:14:52 UTC, Kevin Bailey wrote:

I'm trying to use some fairly simple template argument deduction, but
maybe I'm not getting the syntax correct. C++ doesn't event blink at
something like this, but D is giving me:

temptest.d(18): Error: template temptest.func cannot deduce function from argument types !()(bar), candidates are:
temptest.d(10): func(T)(foo!T.bar f)

I guess D can't crack open a type like that?

template foo(T)
{
class bar
{
        T t;
}

}

void func(T)(            // 10
        foo!(T).bar f)
{
}

int main()
{
        foo!int.bar fi;
        func(fi);        // 18
}

This work:

template foo(T){
        class bar{
    		T t;
        }
    }

void func(alias F : foo!T, T)(F.bar f){
}

void main(){
    	
    foo!int.bar fi;
    func(fi);

}

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