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digitalmars.D.learn - Declaring constant references in struct members

reply David Zhang <straivers98 gmail.com> writes:
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.
}
Feb 15 2017
next sibling parent reply Adam D. Ruppe <destructionator gmail.com> writes:
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
Feb 15 2017
parent reply David Zhang <straivers98 gmail.com> writes:
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
Feb 15 2017
parent Adam D. Ruppe <destructionator gmail.com> writes:
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;
Feb 15 2017
prev sibling parent "H. S. Teoh via Digitalmars-d-learn" <digitalmars-d-learn puremagic.com> writes:
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.
Feb 15 2017