Extension methods

[Neal Gafter]

On Fri, Nov 20, 2009 at 5:34 PM, Rémi Forax <forax at univ-mlv.fr> wrote:

>  Le 21/11/2009 00:52, Neal Gafter a écrit :
>
> On Fri, Nov 20, 2009 at 3:30 PM, Rémi Forax <forax at univ-mlv.fr> wrote:
>
>> There is a real problem of performance with extension methods
>> (at least with Hotspot).
>> Extension methods create megamorphic call sites
>> and Hotspot is not able to inline them.
>>
>
> Extension methods are most simply formulated are static methods (as in C#),
> and are therefore not polymorphic at runtime at all.  They can even be
> inlined trivially.  Such a formulation enables existing methods (such as
> those in Collections and Arrays) to be retrofitted as extension methods as
> well.
>
>
> The problem is not at call site of the extension method but call sites in
> the extension method.
>

If the extension method is inlined, which it usually should be in
performance-critical code (especially for the uses we've been considering),
it's no worse than an ordinary virtual method.