The docs for Proc#arity state:
prc.arity → fixnum: Returns the number of arguments that would not be ignored. If the block is declared to take no arguments, returns 0. If the block is known to take exactly n arguments, returns n. If the block has optional arguments, return -n-1, where n is the number of mandatory arguments. A proc with no argument declarations is the same a block declaring || as its arguments.
Proc.new {}.arity #=> 0
Proc.new {||}.arity #=> 0
Proc.new {|a|}.arity #=> 1
Proc.new {|a,b|}.arity #=> 2
Proc.new {|a,b,c|}.arity #=> 3
Proc.new {|*a|}.arity #=> -1
Proc.new {|a,*b|}.arity #=> -2
Let's try it:
raganwald:2008-11-07 raganwald$ ruby -v
ruby 1.8.6 (2008-03-03 patchlevel 114) [universal-darwin9.0]
raganwald:2008-11-07 raganwald$ irb
>> Proc.new {}.arity
=> -1
>> Proc.new {||}.arity
=> 0
>> Proc.new {|*a|}.arity
=> -1
I guess I need to find another way of detecting a proc with no argument declarations. At least until known issue 574 is resolved.
update
I thought I'd have a look at method arity as well:
class Foo
def no_args
end
end
Foo.module_eval { define_method :no_args_2 do; end }
Foo.instance_method(:no_args).arity
=> 0
Foo.instance_method(:no_args_2).arity
=> -1
It seems that if you explicitly define a method taking no parameters, you get the correct arity. However, if you use define_method and a block, you get the bug again.
Recent work:
- "CoffeeScript Ristretto", "Kestrels, Quirky Birds, and Hopeless Egocentricity" and my other books.
- Cafe au Life, a CoffeeScript implementation of Bill Gosper's HashLife written in the Williams Style.
- Katy, a library for writing fluent CoffeeScript and JavaScript using combinators.
- Method Combinators, a CoffeeScript/JavaScript library for writing method decorators, simply and easily.