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
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
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
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
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