Multiple alias this is coming.

[IgorStepanov via Digitalmars-d-announce]

On Friday, 19 September 2014 at 05:52:53 UTC, deadalnix wrote:
> On Thursday, 18 September 2014 at 11:20:49 UTC, IgorStepanov 
> wrote:
>> I've created pull request, which introduces multiple alias 
>> this.
>> https://github.com/D-Programming-Language/dmd/pull/3998
>> Please see the additional tests and comment it.
>
> What is the policy to resolve conflict ?
>

I wrote about that:

>struct Foo
>{
>    string s;
>    int i;
>
>    alias s this;
>    alias i this;
>}
>
>Foo f = {"foo", 42};
>string s = f; //s == "foo"
>int i = f; //i == 42
>
>If there are many different ways to resolve alias this then 
>error is raised:
>
>struct Bar
>{
>    double d;
>    int i;
>
>    alias d this;
>    alias i this;
>}
>
>Foo f = {1.0, 42};
>double d = f; //Error: compiler doesn't know, f.d or f.i do you 
>want.
>
>In the next expamle, compiler can resolve conflict:
>
>struct Base1
>{
>    int i;
>
>    alias i this;
>}
>
>struct Base2
>{
>    int i;
>
>    alias i this;
>}
>
>struct Derived
>{
>    Base1 b1;
>    Base2 b2;
>    int i;
>
>    alias b1 this;
>    alias b2 this;
>    alias i this;
>}
>
>Derived d = Derived(Base1(1), Base2(2), 3);
>int i = d; //i == 3;
>This done because Derived author know, how to cast his struct to 
>int, and if he say alias i this; this alias hide aliases in base 
>types.
>
>However, if base type contains alias this to another acceptable 
>type, and derived typ hasn't exactly castable alias this then 
>error will be raised:
>
>struct Base1
>{
>    short s;
>
>    alias s this;
>}
>
>struct Base2
>{
>    int i;
>
>    alias i this;
>}
>
>struct Derived
>{
>    Base1 b1;
>    Base2 b2;
>    int i;
>
>    alias b1 this;
>    alias b2 this;
>    alias i this;
>}
>
>Derived d = Derived(Base1(1), Base2(2), 3);
>int i = d; //Ok i == 3;
>long l = d; //Error: what do you want? d.i or d.b1.s?