Re: Declaring constant references in struct members

2017-02-15 Thread Adam D. Ruppe via Digitalmars-d-learn 

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;

Re: Declaring constant references in struct members

2017-02-15 Thread David Zhang via Digitalmars-d-learn 
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

Re: Declaring constant references in struct members

2017-02-15 Thread H. S. Teoh via Digitalmars-d-learn 
On Thu, Feb 16, 2017 at 12:43:30AM +, 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.

Re: Declaring constant references in struct members

2017-02-15 Thread Adam D. Ruppe via Digitalmars-d-learn 

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

Declaring constant references in struct members

2017-02-15 Thread David Zhang via Digitalmars-d-learn 

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.
}