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class Proc
Parent: Object
Version: 1.6

Index:

new [ ] arity call

Proc objects are blocks of code that have been bound to a set of local variables. Once bound, the code may be called in different contexts and still access those variables.

def genTimes(factor)
  return Proc.new {|n| n*factor }
end
times3 = genTimes(3)
times5 = genTimes(5)
times3.call(12) -> 36
times5.call(5) -> 25
times3.call(times5.call(4)) -> 60

class methods
new Proc.new [{ block } ] -> aProc
Creates a new Proc object, bound to the current context. It may be called without a block only within a method with an attached block, in which case that block is converted to the Proc object.

def procFrom
  Proc.new
end
aProc = procFrom { "hello" }
aProc.call -> "hello"

instance methods
[ ] prc[ [params]* ] -> anObject
Synonym for Proc.call.
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 -> -1
Proc.new {|a|}.arity -> -2
Proc.new {|a,b|}.arity -> 2
Proc.new {|a,b,c|}.arity -> 3
Proc.new {|*a|}.arity -> -1
Proc.new {|a,*b|}.arity -> -2

call prc.call( [params]* ) -> anObject
Invokes the block, setting the block's parameters to the values in params using the same rules as used by parallel assignment. Returns the value of the last expression evaluated in the block.

aProc = Proc.new {|a, *b| b.collect {|i| i*a }}
aProc.call(9, 1, 2, 3) -> [9, 18, 27]
aProc[9, 1, 2, 3] -> [9, 18, 27]

Extracted from the book "Programming Ruby - The Pragmatic Programmer's Guide"
Copyright © 2000 Addison Wesley Longman, Inc. Released under the terms of the Open Publication License V1.0.
This reference is available for download.