Compile time performance for metaprogramming is somewhat inconsistent

[John Colvin via Digitalmars-d]

On Thursday, 3 March 2016 at 02:03:01 UTC, maik klein wrote:
> Consider the following code
>
> void main()
> {
>     import std.stdio;
>     import std.range: iota, join;
>     import std.algorithm.iteration: map;
>     import std.conv: to;
>     import std.meta: aliasSeqOf, staticMap, AliasSeq;
>     enum types = "AliasSeq!(" ~ iota(0,10000).map!(i => 
> to!string(i)).join(",") ~ ")";
>     alias t = AliasSeq! (mixin(types));
>     //alias t1 = aliasSeqOf!(iota(0, 10000));
> }
>
> 't' compiles on my machine in ~3.5 seconds while 't1' needs ~1 
> minute to compile. It seems that mixins are just way more 
> performant than template instantiations. Any ideas why? What 
> causes the slowdown and what can I improve?

What happens if you add a few extra branches to 
std.meta.aliasSeqOf, e.g. 
https://github.com/D-Programming-Language/phobos/commit/5d2cdf103bd697b8ff1a939c204dd2ed0eec0b59

Only a linear improvement but maybe worth a try?