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def output name=((default=true); "caius")
puts "name: #{name.inspect}"
puts "default: #{default.inspect}"
# >> name: "caius"
# >> default: true
output "avdi"
# >> name: "avdi"
# >> default: nil

this is one of the weirdest ruby thing's I've ever seen. I love it.

xoxo @ngauthier


caius commented Dec 28, 2011

I love it too, because I can understand how ruby evaluates it (I think.) The default argument is evaluated as ruby, but in the same scope as the method, so setting local variables means they're set for the method as well. And the parenthesis make it one expression, which ruby is fine with. And then it uses the return value of that expression for the default value of the name variable.

teoulas commented Dec 28, 2011

Wow, really interesting. Never thought about this use case, but kind of makes sense.

avdi commented Dec 28, 2011

Holy crap, look at all the forks! You've created a monster!

@caius @avdi - what is the use case of this trick ?

avdi commented Dec 28, 2011

The only use case I can think of is lulz. I'd never let this through a code review.

@avdi :) I was scratching if I would ever end up using this trick...

turbo lulz:

def x y=((return 'lol'); y)

trololo @ngauthier


def x(y=(raise 'i <3 params')); y; end

skanev commented Dec 29, 2011

Don't forget:

def foo(something = (def foo(*); 'bar'; end)) 'qux' end

puts foo(10)  # qux
puts foo      # qux
puts foo(10)  # bar
puts foo      # bar
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