Changing the class data underneath some reference

A Guy With a Question aguywithanquestion at gmail.com
Thu Nov 30 02:32:27 UTC 2017


On Thursday, 30 November 2017 at 00:40:51 UTC, David Colson wrote:
> Hello all!
>
> I'm getting settled into D and I came into a problem. A code 
> sample shows it best:
>
> class SomeType
> {
>     string text;
>     this(string input) {text = input;}
> }
>
>
> void main()
> {
>     SomeType foo = new SomeType("Hello");
>
>     SomeType bar = foo;
>
>     foo = new SomeType("World");
>
>     writeln(bar.text); // Prints hello
>     // I'd like it to print World
> }
>
> In the C++ world I could do this using pointers and changing 
> the data underneath a given pointer, but I can't use pointers 
> in D, so I'm not sure how I can get this behaviour?
>
> I'd be open to other ways of achieving the same affect in D, 
> using more D like methods.

You are dealing with a reference type. Reference types can be 
though of as a value type of an address. The new operator can be 
though of as giving the variable a new address. This means the 
foo and bar variables are not bound to the same value because 
their referencing different address. You need a struct. Which 
isn't a reference.


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