Class

Proc

Inheritance
< Object

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 gen_times(factor)
     return Proc.new {|n| n*factor }
   end

   times3 = gen_times(3)
   times5 = gen_times(5)

   times3.call(12)               #=> 36
   times5.call(5)                #=> 25
   times3.call(times5.call(4))   #=> 60

Methods

Class

Visibility Signature
public new (...)

Instance

Visibility Signature
public == (p1)
public [] (...)
public arity ()
public binding ()
public call (...)
public clone ()
public to_proc ()
public to_s ()

Class Method Detail

Proc.new {|...| block } => a_proc
Proc.new => a_proc

Creates a new Proc object, bound to the current context. Proc::new 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 proc_from
     Proc.new
   end
   proc = proc_from { "hello" }
   proc.call   #=> "hello"

Instance Method Detail

prc == other_proc => true or false

Return true if prc is the same object as other_proc, or if they are both procs with the same body.

prc.call(params,...) => obj
prc[params,...] => obj

Invokes the block, setting the block‘s parameters to the values in params using something close to method calling semantics. Generates a warning if multiple values are passed to a proc that expects just one (previously this silently converted the parameters to an array).

For procs created using Kernel.proc, generates an error if the wrong number of parameters are passed to a proc with multiple parameters. For procs created using Proc.new, extra parameters are silently discarded.

Returns the value of the last expression evaluated in the block. See also Proc#yield.

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

produces:

   prog.rb:5: wrong number of arguments (3 for 2) (ArgumentError)
    from prog.rb:4:in `call'
    from prog.rb:5

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

prc.binding => binding

Returns the binding associated with prc. Note that Kernel#eval accepts either a Proc or a Binding object as its second parameter.

   def fred(param)
     proc {}
   end

   b = fred(99)
   eval("param", b.binding)   #=> 99
   eval("param", b)           #=> 99

prc.call(params,...) => obj
prc[params,...] => obj

Invokes the block, setting the block‘s parameters to the values in params using something close to method calling semantics. Generates a warning if multiple values are passed to a proc that expects just one (previously this silently converted the parameters to an array).

For procs created using Kernel.proc, generates an error if the wrong number of parameters are passed to a proc with multiple parameters. For procs created using Proc.new, extra parameters are silently discarded.

Returns the value of the last expression evaluated in the block. See also Proc#yield.

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

produces:

   prog.rb:5: wrong number of arguments (3 for 2) (ArgumentError)
    from prog.rb:4:in `call'
    from prog.rb:5

clone()

MISSING: documentation

prc.to_proc → prc

Part of the protocol for converting objects to Proc objects. Instances of class Proc simply return themselves.

prc.to_s => string

Shows the unique identifier for this proc, along with an indication of where the proc was defined.