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Varargs concatenation
Jun 20
monkyyy
Jun 20
monkyyy
June 20
Gravatar of monkyyyPosted by monkyyyReply
monkyyy
Gravatar of monkyyy


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alias seq(T...)=T;
alias a=seq!int;
alias b=seq!float;
alias c=a~b;//seq!(int,float)

alias a=seq!();
a~=int;
a~=float;//seq!(int,float)

Concatenation of vartatic templates will automagically grab their headers and combine them together

If the templates are different then the first one will be used

alias a=seq!int;
alias b=AliasSeq!float;
static assert(is(a~b==seq!(int,float));
static assert(is(b~a==AliasSeq!(float,int));

this will allow pulling out template arguments from a reference

alias badseq(T...)=void;

alias a=badseq!(int,float);
alias b=seq!()~a;//seq!(int,float)

it should work with templated structs/functions

struct sumtype(T...){...}
alias a=seq!()~sumtype!(int,float);//seq!(int,float)
June 21
Gravatar of Richard (Rikki) Andrew CattermolePosted by Richard (Rikki) Andrew Cattermole
in reply to monkyyy		Reply
Richard (Rikki) Andrew Cattermole
Gravatar of Richard (Rikki) Andrew Cattermole
Posted in reply to monkyyy


Reply
On 21/06/2025 7:55 AM, monkyyy wrote:
> alias seq(T...)=T; alias a=seq!int; alias b=seq!float; alias c=a~b;// seq!(int,float)

Note: we can do this today.

```d
import std.meta;

template Foo() {
    alias A = AliasSeq!int;
    A = AliasSeq!(A, float);
    pragma(msg, A); // (int, float)
}

alias Foos = Foo!();
```

Unfortunately alias assign doesn't work outside of the template.
Hence the template.

> alias badseq(T...)=void; alias a=badseq!(int,float); alias b=seq!()~a;//
> seq!(int,float)

That can't work, the alias goes bye bye, and it will only see the void.
June 20
Gravatar of monkyyyPosted by monkyyy
in reply to Richard (Rikki) Andrew Cattermole		Reply
monkyyy
Gravatar of monkyyy
Posted in reply to Richard (Rikki) Andrew Cattermole


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On Friday, 20 June 2025 at 20:03:29 UTC, Richard (Rikki) Andrew Cattermole wrote:
> 
> > alias badseq(T...)=void; alias a=badseq!(int,float); alias
> b=seq!()~a;//
> > seq!(int,float)
>
> That can't work, the alias goes bye bye, and it will only see the void.

I think the spec says it *may* but Im pretty sure it *cant* in practice, the inherent memoization exists somewhere

```d
template badseq(T...){
    pragma(msg,T.stringof);
    alias badseq=void;
}
unittest{alias a=badseq!(int,float);}//prints
unittest{alias a=badseq!(int,float);}//doesnt
unittest{alias a=badseq!(int,float);}
unittest{alias a=badseq!(int,float);}
```