DIP66 - Multiple alias this

[Steven Schveighoffer via Digitalmars-d]

On 10/10/14 6:10 PM, IgorStepanov wrote:
> On Friday, 10 October 2014 at 21:26:49 UTC, Steven Schveighoffer wrote:

>> An example:
>>
>> foo(T)(T t) if(is(T : int))
>> {
>>    someFuncThatTakesInt(t);
>> }
>>
>> foo(T)(T t) if(!is(T : int) && is(T.shadow : int))
>> {
>>    someFuncThatTakesInt(t.shadow);
>> }
>>
>> struct A
>> {
>>    int i;
>>    alias i this;
>> }
>>
>> struct B
>> {
>>    int i;
>>    alias i this;
>> }
>>
>> struct C
>> {
>>    A a;
>>    B shadow;
>>    alias a this;
>>    alias shadow this;
>> }
>>
>> C c;
>> foo(c); // should compile, but I think your DIP makes it fail due to
>> ambiguity
>>
>
> You can write foo(c.shadow); This isn't hard.
> Ok, I understood you, let's listen to what others say

Right, you can get around it.

But the issue here is, that I feel like is(T: U) means (from dlang.org):

is ( Type : TypeSpecialization )
The condition is satisfied if Type is semantically correct and it is the 
same as or can be implicitly converted to TypeSpecialization.

This means is(C : int) should indicate that C can implicitly convert to 
int. But in your DIP, it does not. I think this is incorrect.

-Steve