On 22/10/2010 15:24, Jonas Maebe wrote:
On 22 Oct 2010, at 15:09, Martin wrote:
On 22/10/2010 12:28, Jonas Maebe wrote:
AFAIK "constref" was invented for passing values to external subroutines, that expect a reference.
In how far does "constref" affect the *caller*, in contrast to e.g. "var"? Can constref
pass properties, which are not allowed as var parameters?
Right now it's allowed (if the property uses a getter, the getter is called and
its result is put into a temp location whose address is passed), but I think
that's a bug in the implementation.
Why?
Because it's not possible to pass a reference to a property.
True, but that only matters if you intend to change the value of the
property, by changing the value that the reference points to.
const and constref do not make the promise that the refereed value can
be used to change the original value
If I understand correctly:
const: is merely a hint, without any further promise. It allows fpc to
assume the receiver is not going to attempt to change the value. (used
for ansistring, by omitting increasing the ref count). So, even const
could pass a reference to a temporary copy, without breaking any
documented behaviour.
constref: is the same hint, combined with the promise of a reference.
That is the expectation is that the receiver can read the value via a
pointer.
That is also that fpc can act as if the receiver was not going to
change the value, therefore if the reference points to a temporary copy
of the value, the documented behaviour is still fulfilled?
Martin
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