AA value returned by ref function (comments needed)

[Maxim Fomin]

In the 9498 issue there is a discussion about such code:

string[string] myValues;

ref string getValue(string v) {
    return myValues[v];
}

void main() {
    getValue("myValue") = "myString";
}

Currently it throws range violation as myValues[v] is regarged as 
rvalue (in Andrei's notion it is a read operation).

On the one hand, returning some value from AA array is a read 
operation which should throw as it happens with non-ref function. 
It is also impossible to know whether some new value would be 
assigned or just be copied like this:

string s = getValue(); // obviously read operation which need 
throw.
tl;dr it does not really matter how value is returned, only 
whether is exists or not.

On the other hand, as original code shows, it could be write 
operation, so function should not throw.

Spec is silent about this and TDPL barely discusses it, let alone 
ref corner case.

Thoughts?

http://d.puremagic.com/issues/show_bug.cgi?id=9498