alias this and struct initializer

[Adam D. Ruppe via Digitalmars-d-learn]

On Thursday, 18 May 2017 at 08:40:39 UTC, Andre Pany wrote:
> I think as case 2 is working case 3 should work also.

Nope, case 2 is assigning to an already constructed object and 
case 3 is constructing a new one.

alias this is NEVER used in construction. It can only apply after 
the object already exists, just like subclasses vs interfaces. 
Once the object exists, you can assign a subclass to an 
interface, but you can't do

SubClass obj = new Interface();

in theory, the compiler could see the left hand side and know it 
is supposed to be SubClass, but it doesn't - you need to 
construct the class explicitly.

Same with alias this, it allows implicit conversion TO the type 
and assignment of the member through the existing variable (the 
existing variable must already be valid, it is already 
constructed, so it is no different than assigning any other 
public member), but not implicit conversion FROM the type since 
the new struct may have other members that need to be initialized 
too.