Slicing AliasSeq-s

[Adam D. Ruppe via Digitalmars-d]

On Monday, 21 December 2015 at 09:06:08 UTC, Shriramana Sharma 
wrote:
> Both the above page and http://dlang.org/phobos/std_meta.html 
> refer to "slicing" alias sequences. In D slicing means just 
> creating another reference to the same memory as the sliced 
> object.

AliasSeqs have no memory at runtime. They are a compile-time only 
construct.

> So out of curiosity I'd like to know how this is implemented in 
> the compiler: as really a slice or a copy? (Posting this to D 
> and not learn since it relates to compiler internals.)

Check the source! expression.d has class SliceExp. Look down to 
where it handles tuples (AliasSeq is the user-visible name for 
what the compiler internally calls a tuple).

Slicing a tuple creates a new tuple that refers to the same 
objects as the previous one. So it doesn't deep copy... but 
remember this is irrelevant to any D program because an AliasSeq 
is just a compile-time list of constants anyway and thus cannot 
be modified and does not actually have a memory address in the 
generated program anyway.