Segment violation (was Re: Why I could not cast string to int?)

[Alex Rønne Petersen]

On 03-02-2012 11:08, Artur Skawina wrote:
> On 02/03/12 00:20, Jonathan M Davis wrote:
>> in is pointless on value types. All it does is make the function parameter
>> const, which really doesn't do much for you, and in some instances, is really
>> annoying. Personally, I see no point in using in unless the parameter is a
>> reference type, and even then, it's often a bad idea with reference types,
>> because in is really const scope, and the scope is problematic if you want to
>> return anything from that variable. It's particularly problematic with arrays,
>> since it's frequently desirable to return slices of them, and scope (and
>> therefore in) would prevent that. It's useful in some instances (particularly
>> with delegates), but I'd use in _very_ sparingly. It's almost always more
>> trouble than it's worth IMHO.
>
> BTW, scope should have been the default for *all* reference type function
> arguments, with an explicit modifier, say "esc", required to let the thing
> escape. It's an all-or-nothing thing, just like immutable strings - not using
> it everywhere is painful, but once you switch everything over you get the
> benefits.
>
> If it isn't obvious why - GC. The compiler can optimize the cases where it
> knows a newly allocated object can't escape and reduce or omit the GC overhead.
> And yes, it can also do this automatically - but that requires analyzing the
> whole call chain, which is a) not always possible and b) much more expensive.
>
> artur

It is not that simple.

If the class's constructor passes 'this' off to some arbitrary code, 
this optimization breaks completely. You would need whole-program 
analysis to have the slightest hope of doing this optimization correctly.

--
- Alex