Better AAs

[Tom Compton via Digitalmars-d]

On Sunday, 6 July 2014 at 22:53:56 UTC, bearophile wrote:

> Rust has not done the significant D design mistake of putting 
> the associative arrays inside the language/runtime, but D AAs 
> are getting better.

Can someone explain why having AA's builtin to the language is 
such a bad thing. I would have thought that it is a good thing 
because of greater efficiency.