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. Keyword arguments will be considered as a single
additional argument, that argument being mandatory if any keyword argument
is mandatory. For methods written in C, returns -1 if the call takes a variable number of arguments.
class C
def one; end
def two(a); end
def three(*a); end
def four(a, b); end
def five(a, b, *c); end
def six(a, b, *c, &d); end
def seven(a, b, x:0); end
def eight(x:, y:); end
def nine(x:, y:, **z); end
def ten(*a, x:, y:); end
end
c = C.new
c.method(:one).arity #=> 0
c.method(:two).arity #=> 1
c.method(:three).arity #=> -1
c.method(:four).arity #=> 2
c.method(:five).arity #=> -3
c.method(:six).arity #=> -3
c.method(:seven).arity #=> -3
c.method(:eight).arity #=> 1
c.method(:nine).arity #=> 1
c.method(:ten).arity #=> -2
"cat".method(:size).arity #=> 0
"cat".method(:replace).arity #=> 1
"cat".method(:squeeze).arity #=> -1
"cat".method(:count).arity #=> -1
