Optional named arguments in Mathematica

Question

What\'s the best/canonical way to define a function with optional named arguments? To make it concrete, let\'s create a function foo with named arguments a

Answer 1

I'll throw this possible solution into the mix:

foo[opts___Rule] := Module[{f},
  f@a = 1; (* defaults... *)
  f@b = 2;
  f@c = 3;
  each[a_->v_, {opts}, f@a = v];

  Return[bar[f@a, f@b, f@c]]
]

I like it for its terseness but I don't think it's the standard way. Any gotchas with doing it that way?

PS, it uses the following handy utility function:

SetAttributes[each, HoldAll];                (* each[pattern, list, body]     *)
each[pat_, lst_, bod_] :=                    (*  converts pattern to body for *)
  Scan[Replace[#, pat:>bod]&, Evaluate@lst]  (*   each element of list.       *)