From: "Jon A. Lambert" <jlsysinc@...>
Date: 2003-12-15T09:52:50+09:00
Subject: Arity?

From the Programming Ruby - The Pragmatic Programmer's Guide:

--class Proc ---
arity  prc.arity -> anInteger

Returns the number of arguments required by the block. If the block
takes no arguments, returns -1. If it takes one argument, returns -2.
Otherwise, returns a positive argument count unless the last argument
is prefixed with *, in which case the argument count is negated. The
number of required arguments is anInteger for positive values, and
( anInteger +1).abs otherwise.

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

--class Method --

arity  meth.arity -> aFixnum

Returns an indication of the number of arguments accepted by a method.
Returns a nonnegative integer for methods that take a fixed number of
arguments. For Ruby methods that take a variable number of arguments,
returns -n-1, where n is the number of required arguments. For methods
written in C, returns -1 if the call takes a variable number of arguments.

----

I can make neither head nor tail of this as the values that are actually returned
are not those in the example, and the text doesn't appear to make any sense at
all to me.  Can someone explain what arity means and how it's determined?

--
J. Lambert