DIP 1021--Argument Ownership and Function Calls--Community Review Round 1

[Mike Franklin]

Consider this contrived example:

someLibrary.d
-------------
module someLibrary;

import core.stdc.stdlib;

int a;
int b;

ref int foo() @safe
{
     if ((rand() % 2) == 0)
     	return a;
     else
     	return b;
}

ref int bar() @safe
{
     if ((rand() % 4) == 0)
     	return a;
     else
     	return b;
}

main.d
------
import someLibrary;

void doSomething(scope ref int a, scope ref int b) @safe
{
     // whatever...
}

void main() @safe
{
     doSomething(foo(), bar());
}

How can the compiler statically determine whether `foo` and `bar` 
will return a reference to the same data?

It seems the language or type system must provide this guarantee, 
which would require a full-fledged ownership/borrowing system to 
accurately enforce what this DIP is proposing.