Multiple alias this is coming.

[IgorStepanov via Digitalmars-d-announce]

On Thursday, 18 September 2014 at 22:16:23 UTC, bearophile wrote:
> IgorStepanov:
>
>> Do you ask about alias this or about it multiple usage. 
>> Multiple usage is similar to single, but multiple:)
>
> I meant the multiple usage. And none of your examples here are 
> use cases :-( I'd like to see one use case, or more.
>
> Bye,
> bearophile

For example, you can define struct (value-type with automatic
storage class) which implements interfaces:

intarface InputStream
{
     ...
}

intarface OutputStream
{
     ...
}
struct File
{
     this(string name, string options)
     {
         impl = new FileImpl(name, options);
     }

     ~this()
     {
         impl.close();
     }

     @property InputStream inputStream()
     {
        return new class(impl) InputStream
        {
            //InputStream implementation
            ...
        }
     }

     @property OutputStream outputStream()
     {
        return new class(impl) OutputStream
        {
            //OutputStream implementation
            ...
        }
     }

     alias inputStream this;
     alias seekable this;
     FileImpl* impl;
}


Record[] readData(InputStream);
void storeData(OutputStream, Record[]);

Record[] extractRecords()
{
     File f = File("records.bin", "rw");
     auto data = readData(f);
     ///split to extracted and remaining
     f.truncate();
     writeData(f, remaining);
     return extracted;
}