Feature request: Allow don't care `_` as default argument for out arguments

[apinski-cavium]

Personnel

• [x] Owner: @apinski-cavium
• [x] Supporters: @mbudiu-vmw

Design

• [x] Document: See below

Implementation

• [ ] p4-spec:
• [ ] p4c:

Process

• [ ] LDWG discussed:
• [ ] LDWG approved:
• [ ] Merged into p4-spec:
• [ ] Merged into p4c:

=======================================

It would be a good idea to allow don't care _ as default arguments for out arguments so you don't need to specify them when doing the call. I can see cases where it would be useful in the general sense. An example of simple usage would be like:

void f(out bit a = _){ a = 1; }
void g(out bit b)
{
  f();
  f(b);
}

You could do this right now with a wrapper function:

void f(out bit a){ a = 1; }
void f(){ f(_); }
void g(out bit b)
{
  f();
  f(b);
}

So it just becomes a nice feature of the language.

[mihaibudiu]

Solved by https://github.com/p4lang/p4-spec/pull/1074

[apinski-cavium]

Solved by #1074

Huh? No that is a different feature request unrelated to this one. That only just solves f(a = _); for the call. I am asking for calls like f(); where the default argument was don't care.

[jnfoster]

In the interest of tidying up the set of active issues on the P4 specification repository, I'm marking this as "stalled" and closing it. Of course, we can always re-open it in the future if there is interest in resurrecting it.