default arguments order

gistfile1.txt

# non-default params = true arity; 
# args <= arity: apply args to non-defaults first, in order
# args >  arity: apply args in order


f = (a=0,b,c=2) ->
f()      # a = 0 b = undefined c = 2
f(1)     # a = 0 b = 1 c = 2
f(1,2)   # a = 1 b = 2 c = 2
f(1,2,3) # a = 1 b = 2 c = 3

f = (a=0,b,c,d=3) ->
f()        # a = 0 b = undefined c = undefined d = 3
f(1)       # a = 0 b = 1 c = undefined d = 3
f(1,2)     # a = 0 b = 1 c = 2 d = 3
f(1,2,3)   # a = 1 b = 2 c = 3 d = 3
f(1,2,3,4) # a = 1 b = 2 c = 3 d = 4

Ew. I would not like this behaviour.

Hah! I initially wrote 'ick' at the bottom. I had thought this behavior would be handy a few times recently, and asked jashkenas and brendaneich on twitter:

f = (a=1,b,c=3) ->
f(2) # a = 1, b = 2, c = 3

brendaneich said "what about f(1,2)". The above was me reasoning out how it'd work and then filing it away here so that I would remember why it wasn't a good idea to propose it for CoffeeScript ;)