On 09/02/13 15:49, Joseph Rushton Wakeling wrote:
> On 02/09/13 15:39, Artur Skawina wrote:
>> While this may not seem ideal, sometimes you do *not* want to do it
>> (when you need to keep the original context), so there are no obvious
>> alternatives that would handle all cases automagically.
>
> I'm sure there are valid use cases where this behaviour is desirable. In
> fact, all approaches to creating reference-type structs rest on this,
> although in those cases the reference is usually a pointer to a payload
> rather than a delegate to a function.
>
> The point is, it's a risk if you don't appreciate how value and reference
> types intermingle -- and even when you do in principle, it's easy to
> accidentally overlook in practice. The Phobos unittests, which for
> RandomSample are very extensive, didn't catch this problem.
Requiring captures to be explicit would reduce the chance of such
bugs happening, but also have a significant cost and be a rather
drastic change to the language...
In this case, there's no need for a delegate, as you do not want
to operate on the original object. So you can simply do:
//...
private void function(ref typeof(this)) _jump;
private void jump() { _jump(this); }
this(size_t max)
{
_max = max;
_jump = &jump10;
}
//...
static jump10(ref typeof(this)this_)
{
this_._count += 10;
writeln("At end of jump, count = ", this_._count);
}
It's cheaper than the other alternative (updating ctx in cpctor),
but slightly more verbose. More importantly, AFAICT, this is a
better fit for the actual problem.
artur
