Fastest Way of Accessing Entries in an AA

[Jonathan M Davis via Digitalmars-d-learn]

On Friday, January 09, 2015 00:20:07 Foo via Digitalmars-d-learn wrote:
> On Thursday, 8 January 2015 at 23:06:39 UTC, Nordlöw wrote:
> > On Thursday, 8 January 2015 at 16:11:07 UTC, ketmar via
> > Digitalmars-d-learn wrote:
> >> how can it? compiler doesn't know what the code is supposed to
> >> do. if
> >> compilers will know such things someday, we can stop writing
> >> programs
> >> altogether, as compilers will be able to write any program for
> >> us. ;-)
> >
> > Correction:
> >
> > I thought it would be nice if the compiler explained to me that
> >
> >     key in aa ? aa[key]
> >
> > is a sub-optimal performance-wise.
>
> You know, that you kan reuse the result of the in operator by AAs?
>
> example:
>
> auto ptr = key in aa;
> ptr ? *ptr : ValueType.init

This idiom is quite common:

if(auto ptrToValue = key in aa)
{
}

though I'm not sure that that quite fits in with what Nordlow seems to be
trying to do with init. aa.get probably does a better job of that, though
looking at the implementation for get, it's basically doing what you're
suggesting:

auto p = key in aa;
return p ? *p : defaultValue;

though that has the downside of using a lazy parameter for the default
value, which is convenient but doesn't do great things for performance.

- Jonathan M Davis