default arguments for functions? about coffeescript HOT 9 CLOSED

This has come up a couple of times. Here's my pasted answer from an earlier email:

I fiddled with default arguments for a while, but there are a number
of problems. It significantly complicates the grammar to allow arbitrary
expressions within parameter lists. Function literals look really
confusing with objects and assignment in the parameter lists, because
the "=>" gets lost in all the noise. And most of all, default arguments
aren't so much of an issue in JavaScript in the first place. You need to
use them in Ruby in order to create a method that's able to take
variable numbers of arguments, but JavaScript has no such problem
-- any method can be called with any number of named arguments. Providing
the default can be done quite easily with "||=". If CoffeeScript has both
variable argument length and "||=", putting the defaults up top in the
parameter list just makes things harder to read, without providing any
functionality that couldn't be otherwise accomplished.

But that's kind of just a rationalization for something that looks pretty ugly when shoehorned into CoffeeScript's syntax. I like using them in Ruby too. So if anyone comes up with a gorgeous syntax that wouldn't be too hard to parse, I wouldn't be opposed.

from coffeescript.

how about switching => to -->, then it won't get confused so with other ='s

mymeth: a="abc", b="def" --> a + b

I kind of like it as well as its slightly bigger (and no harder to type).

from coffeescript.

mymeth: a | "abc", b | "def" => a + b

from coffeescript.

Well, = is kind of an opt-in assignment operator anyway, isn't it?

It's not that bad when you use the proper Coffee colon:

mymeth: a:"abc", b:"def" => a + b

from coffeescript.

I agree with @noonat, actually.

mymeth: a:"abc", b:"def" => a + b

seems much nicer than

mymeth: a, b => (a or "abc") + (b or "abc")

and any other syntax would just add unnecessary complexity.

from coffeescript.

My original objection was just that it looks too confusing with all the assignment, especially when the method signature is longer. And, that while in Ruby it serves a real purpose (calling the function with more or fewer named arguments), in JavaScript you can always already do that. Do y'all really prefer this:

any: obj, iterator: _.identity, context: undefined =>
  return obj.some().....

To this:

any: obj, iterator, context =>
  iterator ||= _.identity
  return obj.some().....

If I wasn't already familiar with default arguments, I'd have a hard time understanding what was going on in the first one.

from coffeescript.

I agree that the addition of the ||= operator means this is not really a necessary feature.

from coffeescript.

Ok. Closing the ticket. If anyone finds a really readable syntax for this for methods with long signatures, feel free to reopen it.

from coffeescript.

I have implemented this in my default_args branch. Syntax is pretty simple:

fn: (param1, param2: 'default value', param3: param1 + param2) ->
  # param1 can be null or undefined
  # param2 is defaulted to 'default value' is omitted or null
  # param3 is the value of param1 and param2 after param2 has been defaulted

from coffeescript.