Hi,

Say I have a struct S that holds a reference to an object O. Is there a way to express that I want to be able to change the reference, but not what the reference points to? Thanks.

struct S {
    O object;
}

class O {
    size_t things.
}

On Thu, Feb 16, 2017 at 12:43:30AM +0000, David Zhang via Digitalmars-d-learn wrote:
> Hi,
> 
> Say I have a struct S that holds a reference to an object O. Is there a way to express that I want to be able to change the reference, but not what the reference points to? Thanks.
> 
> struct S {
>     O object;
> }
> 
> class O {
>     size_t things.
> }

Maybe have a look at std.typecons.Rebindable?


T

-- 
What do you call optometrist jokes? Vitreous humor.

On Thursday, 16 February 2017 at 00:43:30 UTC, David  Zhang wrote:
> struct S {
>     O object;
> }

import std.typecons;

Rebindable!O object;

http://dpldocs.info/experimental-docs/std.typecons.Rebindable.html

On Thursday, 16 February 2017 at 00:49:45 UTC, Adam D. Ruppe wrote:
> On Thursday, 16 February 2017 at 00:43:30 UTC, David  Zhang wrote:
>> struct S {
>>     O object;
>> }
>
> import std.typecons;
>
> Rebindable!O object;
>
> http://dpldocs.info/experimental-docs/std.typecons.Rebindable.html

Is there a similar mechanism for one struct holding another? Otherwise, you get a cannot modify X with immutable members error.

eg:

struct A {
    B b;
}

struct B {
    const size_t something;
}

A a = A(B(16));

//attempt to replace a.b with new B
a.b = B(32); //error: cannot modify struct a.b B with immutable members

On Thursday, 16 February 2017 at 01:05:58 UTC, David  Zhang wrote:
> Is there a similar mechanism for one struct holding another?

You'd have to make the member a pointer to the struct.


immutable(B)* b;