Daniel Keep wrote:
Sean Kelly wrote:
Daniel Keep wrote:
Andrei Alexandrescu wrote:
Denis Koroskin wrote:
[snip]
get/set/free?
With these you can't move a resource inside the property.
Andrei
Python has an overload for removing properties. In all my years of
using Python, I've *NEVER* once had a use for it, or even worked out why
I'd want to use it.
I'm not saying we shouldn't be able to do this, I just can't see the
need for move/remove for properties; where would this be useful?
Does Python have complex value types?
Sean
You mean these?
(1+2j) * (2+3j)
(-4+7j)
Don't ask me why they used 'j' instead of 'i'. :P
If you mean aggregate types that have value semantics, then no.
He meant the latter (emphasis on the other syllable, I always forget
which is which). This brings back the notion of precision and
efficiency. C++ tries to define operations such that some never throw,
as those can be used in code with transactional semantics. It also tries
to manage resources deterministically, which means there's strict
control over values being created and destroyed. It's hard to combine
these two within a harmonious system.
Anyhow, here's a simple D example. Consider we define a BigInt type as a
value-type struct: when you copy a BigInt to another, the latter becomes
an independent copy:
BigInt a = 100;
BigInt b = a;
++b;
assert(a == 100);
BigInt's copy constructor would allocate memory dynamically, which means
it may throw and also that it is inefficient to copy BigInt objects
unwittingly.
So far, so good. Now say we define some range that iterates over
BigInts. If that range chooses to implement head() as a property, then a
copy is created whenever you ask for head. The small problem is that
that's inefficient. The larger problem is that there is no way to
correctly e.g. sort such a range. Sorting hinges on swap, and with
properties you can't ever swap without risking to throw. Sort would end
up throwing, and not only throwing, but losing state irretrievably while
at it. Well that's not a foundation we want to build D on, do we?
Andrei
