Hello
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 ### <<< error?
Proc.new {|a,b|}.arity » 2
Proc.new {|a,b,c|}.arity » 3
Proc.new {|*a|}.arity » -1
Proc.new {|a,*b|}.arity » -2
I would say it's a typo
Regards, Daniel
and one case is missing there
irb(main):169:0> proc{}.arity
=> -1
which means, all paramers are ignored(right?)
Schüle Daniel wrote:
I forgot to copy&paste the link
http://www.rubycentral.com/book/ref_c_proc.html#Proc.arity
I believe that page refers to Ruby 1.6.
See the docs for 1.8.4:
http://www.ruby-doc.org/core/classes/Proc.html#M000808
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Negative arities indicate the _minimum_ number of args to a proc that takes a variable number of args
min args = abs(arity + 1) if arity < 0 otherwise arity
so a proc with no arg speciafication is the same as proc { |*args| }. (You just can't get at the argument list)
proc { |a, *b| } will have an arity of -2
abs(-2 + 1) = 1 so it must be passed at least one arg
proc { |a, b, c| } will have an arity of 3
proc { || } will have an artity of zero (contrasted with proc { } )
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On Mar 8, 2006, at 10:08 AM, Schüle Daniel wrote:
and one case is missing there
irb(main):169:0> proc{}.arity
=> -1
which means, all paramers are ignored(right?)