Trying to get type and name at compile time

[ag0aep6g via Digitalmars-d-learn]

On 05/24/2016 06:22 PM, Edwin van Leeuwen wrote:
> That's what I assumed at first.. So why does the following fail with:
> cannot interpret double at compile time? I assumed staticMap would
> automatically flatten the resulting AliasSeqs.
>
> ```
> import std.meta : AliasSeq, ApplyLeft, staticMap;
>
> struct Point { double x; double y; }
>
> template addType(T,alias name)
> {
>      alias addType = AliasSeq!( typeof(__traits(getMember, Point, name)),
>          name );
> }
>
> alias test3 = addType!( Point, "x" );
>
> // I expected AliasSeq!(double,"x")???
> pragma(msg,test3); // tuple((double), "x")
>
> //static assert(is(test == AliasSeq!(double,"x")));
> alias ts = AliasSeq!("x","y");
> alias addTypeP = ApplyLeft!(addType,Point);
> alias mapped = staticMap!(addTypeP,ts);
>
> pragma(msg,mapped);
>
> void main() {
> }
> ```

Seems to be a problem in ApplyLeft:

----
import std.meta: AliasSeq, ApplyLeft;
alias addType(T, string name) = AliasSeq!(T, name);
alias addTypeInt = ApplyLeft!(addType, int);
alias FullyInstantiated = addTypeInt!"foo";
----

Fails with: "std/meta.d(1114): Error: cannot interpret int at compile time".

I've filed an issue:
https://issues.dlang.org/show_bug.cgi?id=16070

[...]
> I thought so, but a lot of the documentation does seem to compare it
> (see the example here):
> https://dlang.org/library/std/meta/static_map.html

Using `is(...)` with an AliasSeq of only types is ok. But you can't use 
it when there's a non-type in the sequence.