I dun a DIP, possibly the best DIP ever

[Stefan Koch]

On Friday, 24 April 2020 at 20:55:19 UTC, Walter Bright wrote:
>
> Another approach to resolving the original problem (template 
> instantiation bloat) is for the compiler to recognize templates 
> like AliasSeq as "special" and implement them directly.
>
>
> For example, AliasSeq is defined as:
>
>   template AliasSeq(TList...) { alias AliasSeq = TList; }
>
> This pattern is so simple it can be recognized by the compiler. 
> (Having std.meta.AliasSeq being a special name known to the 
> compiler is not necessary.)
> The compiler already recognizes certain patterns, such as the 
> expression that does a rotate, and then generates the CPU 
> rotate instruction for it.

AliasSeq itself is not the problem at all.
The problem is when operating on AliasSeq you need to instantiate 
new templates to keep them in a "TypeExp" state. Where they can 
still be manipulated as lists.
You detect operations you might do on type lists and implement 
them as special cases in the compiler, but then you end of with 
many specialzed cases which have to treated diffrently.
You push complexity from the langauge into the compiler 
implementation details.
And that's where it shouldn't be because who is going to verify 
that.
People here who are familiar with the c++11 syntax have already 
found bugs.
That won't be possible if it's an unspecified set of rewrites 
that take place in an unspecified stage.