On Thursday, 19 July 2012 at 08:14:25 UTC,
trav...@phare.normalesup.org (Christophe Travert) wrote:
"monarch_dodra" , dans le message (digitalmars.D:172700), a
écrit :
I think it would be better to "initialize on copy", rather
than default initialize. There are too many cases an empty
array is created, then initialized on the next line, or passed
to something else that does the initialization proper.
Not default-initializing Array has a cost for every legitimate
use of an Array.
I'm back pedaling and agreeing 100% actually. Plus it keeps the
implementation simpler. +1 to you.
Keeping the adress of the content secret may be a valuable
intention,
but as long as properties and opIndex does not allow to
correctly
forward methods, this is completely broken. Is there even a
begining of
a plan to implement this? I don't see how properties or opIndex
could
safely forward methods that uses references and that we do not
control
without escaping the reference to them. That's not possible
until D has
a complete control of escaping references, which is not planned
in the
near or distant future. Not to mention that having a complete
control of
escaping reference break lots of code anyway, and might
considerably
decrease the need for ref counted utilities like... Array.
Please, at least give me hope that there is light at the end of
the
tunnel.
One of the reason the implementation doesn't let you escape a
reference is that that reference may become (_unverifiably_)
invalid. Ranges to Arrays, on the other hand, keep a reference to
the Array itself, and always* remain valid. (always as long as
the Array doesn't shrink past the range's boundaries, but in this
case, at least, the range throws an exception, rather than crash
the program).
A reference to a dynamic array, on the other hand, will ALWAYS be
valid 100% of the time, because the original data is never
actually destroyed (until unreferenced). So it is perfectly safe
to expose references in an array.
So escaping references from an Array is something _very_
dangerous, especially in a language that kind of guarantees it
won't core dump if you don't manipulate pointers (which could if
arrays escaped references).
While I get your point, it really feels like a "lose lose"
situation here: You get stiffed either way...with Array...
...That said, I see no reason for the other containers (SList,
I'm looking at you), not to expose references.
The way I see it, Array *could* escape references, but then the
whole class would have to be qualified @unsafe (if such a thing
existed) or something along these lines.
The current work around? Copy-Extract, manipulate, re-insert.
Sucks.
On Thursday, 19 July 2012 at 10:39:56 UTC, Matthias Walter wrote:
On 07/19/2012 10:14 AM, Christophe Travert wrote:
I agree here. Additionally my question: Is it possible (at the
moment)
to really do "initialize on copy"? As far as I see it, the only
way to
interact here is to implement 'this(this)' which is called after
bit-copying and hence cannot access the source of the copy
process.
Good point. The answer is no though. A RefCounted (also known as
SharedPointer in C++) needs to be initialized first if you want
it aliased.
Allowing such a behavior is possible, but prohibitively expensive.
