Re: Pass by Reference
- Posted by petelomax Jan 15, 2015
- 1997 views
What I'm asking for is a level of compile-time safety. Obviously, there's no way to know the number of parameters that are being passed back with a sequence until runtime.
The distinction I'm trying to make is that a function has the option of passing back multiple values. You'd only do this for the purpose of additional compile-time safety.
... I think this must have got lost in all the shouting:
The second can only be determined to be wrong at runtime, and will result in a crash.
It would probably not be difficult to collect min/max/unknown lengths of returned sequences, so as long as you don't build return values using append() etc, it should be just as easy to check (at parse time).
I took a couple of minutes to check, and in my own particular parlance:
- DoRoutineDef() has to initialise a few new static vars/flags
- DoReturn() has to check opstack for opMkSq,N or an all-literal-const-sequence and set those flags/lengths accordingly
- DoRoutineDef() has to save those vars/flags permanently in the symtab, and post-validate any prior fwd calls
- MultipleAssignment() checks opstack for a return var, and either
- logs the forward call for DoRoutineDef() to later process, or
- validates things there and then
As I see it, the only sticky points are
firstly that one = f() is just a plain (sequence) assignment and gets no validation whatsoever, but anything with the {one,...} = f() syntax gets checked, and
secondly that any return not of the return {...} syntax precludes any and all checks on calls-with-multiple-assignment to that particular routine.
Third and last, {} = f() does not trigger a mismatch, as it is an explicit discard.
Pete
