opAssign return type

[Q. Schroll via Digitalmars-d-learn]

On Friday, 2 September 2016 at 17:33:22 UTC, Steven Schveighoffer 
wrote:
> On 9/2/16 1:18 PM, Q. Schroll wrote:
>> When overloading assignment, I've been taught in my C++ course 
>> to return
>> a reference to the lvalue being assigned to. This is easily 
>> possible in
>> D, but in Phobos it is used rarely and in Ali Çehreli's Book 
>> it is
>> neither taught to do so.
>
> Sure, you can do this.
>
>> Is there any reason to it? To me it seems very obvious to do 
>> it like in
>> C++.
>
> I can imagine a reason is to avoid issues with lifetime. It's 
> dangerous to return this as a reference in most cases, because 
> this is implicitly passed by reference even for rvalues.
>
> However, for opAssign, you generally are sure you don't have an 
> rvalue.

Interestingly the compiler does not allow rvalue = expr but it 
does however allow rvalue.opAssign(expr).

> In any case, there's nothing wrong with it technically, it 
> should work.
>
> -Steve

There is no possibility to enforce some method is only available 
for lvalue this?