Re: Pass by Reference
- Posted by jimcbrown (admin) Jan 16, 2015
- 1917 views
I've only just grasped the full extent of the call_func() issue and yes that gets horribly messy because it has to drag all this stuff out of the parser and right into the runtime/translator, for very little benefit.
If desequencing simply mandated that the LHS and the RHS must have the same number of elements, or else it's a run-time error, then simply using desequencing with call_func() would be able to catch most of the errors that the parser's multiple assignment scanner would. Hmm.
If desequencing were just the same as multiple assignment then yes,
I guess this depends on the implementation.
I take it for granted that in desequencing (playing with sequences) this remains perfectly valid
p = {1,2,3} {i,j} = p
Let's take that for the sake of argument.
However, with multiple assignments (function results)
{i,j} = call_func(...) -- (oi, there be 3 values there, mate)
It's ugly (and I mean really ugly), but it's possible to make the desequencing operator aware that the value comes from a call to call_func(), and behave differently in that case. So then,
{i,j} = p -- ok, ignore the third {i,j} = call_func(...) -- run-time error function identity(object o) return o end function {i,j} = identity(call_func(...)) -- a trap! no run-time error!!!
p = call_func(...) -- (oi, where's me multiple assignment)
You got me. This one I don't know how to handle....
Then whether it is desequencing (as above) or the semantically different multiple assignment (function results) must be dynamically determined; whether the routine being invoked contains a return 1,2,3 or a return {1,2,3} has to be known at run-time to determine whether it is an error or not. That is the bit I am calling an awful lot of work for very little gain.
I hadn't even thought of this. I was thinking of ways to do it without having to dynamically determine the difference at run-time (by having it all turn into desequencing at run-time, and then adding some special cases to desequencing to make it look more like multiple assignment).
