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digitalmars.D.learn - opAssign in D2

reply lurker <lurker lurker.com> writes:
hi,

i like to copy objects such as:

class A {....}

A xxx; // some things are done ...

A yyy = xxx;

how can one do that in D2 easy? are any samples?

thanks
Jun 02 2008
next sibling parent BCS <ao pathlink.com> writes:
Reply to lurker,

 hi,
 
 i like to copy objects such as:
 
 class A {....}
 
 A xxx; // some things are done ...
 
 A yyy = xxx;
 
 how can one do that in D2 easy? are any samples?
 
 thanks
 

first, classes are reference types so the above needs to be: A xxx = new A; // some things are done ... A yyy = xxx; second, that assignment will work as is but will act as a reference copy (you get two copies of the reference to the same object). If you want a real copy you can use structs or generate a deep copy function for the class. I don't use 2.0 so someone else will need to fill in the details.
Jun 02 2008
prev sibling parent reply "Koroskin Denis" <2korden gmail.com> writes:
On Mon, 02 Jun 2008 20:08:29 +0400, lurker <lurker lurker.com> wrote:

 hi,

 i like to copy objects such as:

 class A {....}

 A xxx; // some things are done ...

 A yyy = xxx;

 how can one do that in D2 easy? are any samples?

 thanks

You shouldn't use this for by design, it's not supported for reference types, only for structs. But you might consider wrapping the class into a struct with overloaded opAssign semantics. It sould work fine for you (after opImplicitCast is implemented :)). The other limitation of opAssign is that you can't override opAssign to accept object of the same type: T t1; T t2; t1 = t2; // can't be hooked :( Compiler just makes a plain bitwise copy of the object in any case. I was trying to implement C++-style reference (Ref!(T) template), it works fine but the I didn't find any way to disallow reference rebindment: int i = 5; Ref!(int) ri = i; ri = 0; assert(ri == i); --ri; assert(ri == i); ri *= 2; assert(ri == i); ri ^= 4; assert(ri == i); int t = 0; ri = Ref!(int)(&t); // that's what I want to disallow, but can't :( assert(ri == i); Anyone knows how to workaround this?
Jun 02 2008
parent BCS <ao pathlink.com> writes:
Reply to Koroskin,

 On Mon, 02 Jun 2008 20:08:29 +0400, lurker <lurker lurker.com> wrote:
 
 hi,
 
 i like to copy objects such as:
 
 class A {....}
 
 A xxx; // some things are done ...
 
 A yyy = xxx;
 
 how can one do that in D2 easy? are any samples?
 
 thanks
 

types, only for structs. But you might consider wrapping the class into a struct with overloaded opAssign semantics. It sould work fine for you (after opImplicitCast is implemented :)). The other limitation of opAssign is that you can't override opAssign to accept object of the same type:

It's not really clean but making a dup() method would be constant with D's arrays.
Jun 02 2008