Re: Classes new'd inside for loop are all the same instance?
On Thursday, 8 September 2016 at 12:36:29 UTC, drug wrote:
is address of the variable c, that is allocated on the stack
and has the same address on every iteration
cast(void*)c return the value of variable c that is address of
a class instance and is different for every iteration
in other words
is address of pointer
cast(void*)c is the pointer itself
Yes, thank you. I'll just add that in D (as well as in Java and
C#), while classes are always reference types and the type of `c`
in `C c = new C();` will be reported as C, it's actually more of
a hidden type, "reference to a C". These references are always
passed by value.
c (reference to a C) value pointed at by c
on the stack on the heap
[0x2450]... [0x8695]
|^
||
For example:
class C
{
string name;
}
void setName(C c)
{
c.name = "bob"; //This change will be seen outside setName
c = new C("jim"); //This change will not
}
void setNameRef(ref C c)
{
c.name = "bob"; //This change will be seen outside setNameRef
c = new C("jim"); //This change will also be seen outside
setNameRef
}
In `setName` c (which is actually a reference to a C) cannot be
rebound as the reference is passed by value into the function.
However, c.name can still be modified as you are modifying the
value pointed at by the reference, not the reference itself.
In `setNameRef` you can modify both, because c is passed by ref,
meaning that there is now a double-indirection. Thus, you can
modify both c and the value pointed at by c.
Re: Classes new'd inside for loop are all the same instance?
08.09.2016 15:24, lobo пишет:
I am confused, which is normal, but I'd appreciate some help :-)
If I create N classes in a for loop they are all the same instance. I
would expect each to be a unique instance of the class. See the code below
---
class C {}
void main() {
import std.stdio;
auto c1 = new C();
writefln("c1:%s", ); // OK, instance c1 is unique
auto c2 = new C(); // OK, instance c2 is unqiue
writefln("c2:%s", );
foreach(a; 0..10) {
C c = new C(); // All instances are the same object with the
same address?
writefln("c:%s", );
}
}
---
This isn't what I expected. What could I be doing wrong?
Thanks,
lobo
is address of the variable c, that is allocated on the stack and has
the same address on every iteration
cast(void*)c return the value of variable c that is address of a class
instance and is different for every iteration
in other words
is address of pointer
cast(void*)c is the pointer itself
Re: Classes new'd inside for loop are all the same instance?
On Thursday, 8 September 2016 at 12:36:29 UTC, drug wrote: 08.09.2016 15:24, lobo пишет: [...] is address of the variable c, that is allocated on the stack and has the same address on every iteration cast(void*)c return the value of variable c that is address of a class instance and is different for every iteration in other words is address of pointer cast(void*)c is the pointer itself Got it, thank you :)
Re: Classes new'd inside for loop are all the same instance?
On Thursday, 8 September 2016 at 12:28:55 UTC, Meta wrote: On Thursday, 8 September 2016 at 12:24:48 UTC, lobo wrote: [...] I don't have time to explain at the moment, but change the `` to `cast(void*)c` and you will see what you expect. I will post an explanation soon. Thanks for the blazingly quick reply! :) Please post the explanation when you get time because I'd love to know what is really happening. bye, lobo
Re: Classes new'd inside for loop are all the same instance?
On 09/09/2016 12:24 AM, lobo wrote:
I am confused, which is normal, but I'd appreciate some help :-)
If I create N classes in a for loop they are all the same instance. I
would expect each to be a unique instance of the class. See the code below
---
class C {}
void main() {
import std.stdio;
auto c1 = new C();
writefln("c1:%s", ); // OK, instance c1 is unique
auto c2 = new C(); // OK, instance c2 is unqiue
writefln("c2:%s", );
foreach(a; 0..10) {
C c = new C(); // All instances are the same object with the
same address?
writefln("c:%s", );
}
}
---
This isn't what I expected. What could I be doing wrong?
Thanks,
lobo
Well for starters C is already a pointer ;)
cast(void*) should do the trick not &.
Re: Classes new'd inside for loop are all the same instance?
On Thursday, 8 September 2016 at 12:24:48 UTC, lobo wrote:
I am confused, which is normal, but I'd appreciate some help :-)
If I create N classes in a for loop they are all the same
instance. I would expect each to be a unique instance of the
class. See the code below
---
class C {}
void main() {
import std.stdio;
auto c1 = new C();
writefln("c1:%s", ); // OK, instance c1 is unique
auto c2 = new C(); // OK, instance c2 is unqiue
writefln("c2:%s", );
foreach(a; 0..10) {
C c = new C(); // All instances are the same object
with the same address?
writefln("c:%s", );
}
}
---
This isn't what I expected. What could I be doing wrong?
Thanks,
lobo
I don't have time to explain at the moment, but change the ``
to `cast(void*)c` and you will see what you expect. I will post
an explanation soon.
