About ref used for performance reasons with struct

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How about this approach:
You almost need functions, which takes structs as an rvalue, for 
things like:
----
struct A { }
void foo(A a) { }

foo(A());
----
So what's about something like this (Yes I mark it with '&'):
----
struct A { }
void foo(A& a) { }
----
The compiler decides at compile time whether A should be taken by 
ref or by value.
So for example, if A.sizeof > 16, it changes to:
----
void foo(ref A a) {
----
otherwise:
----
void foo(A a) {
----
In the latter case nothing happens for calls like: foo(A());
But in the former case the call:
foo(A());
is changed to:
auto __temp = A(); foo(__temp);