From: Shashank Date <ADATE@...>
Date: 2002-08-06T08:19:41+09:00
Subject: block , yield and proc?

I  am experimenting with code using blocks, yield and proc in Ruby (1.7.2
mswin32) and discovered three different ways of expressing the same idea:

Q1: Why does the following code :

    def tstbloc(&bloc)
       bloc.call 1,2,3
    end

    tstbloc {  |i| puts "got: #{i}"}        # this produces the output as
below
    tstbloc {|i,j| puts "got: #{i}"}        # but this generates an error

produce the following output?

    got: 123

    C:\rbtst\tstbloc.rb:2: wrong number of arguments (3 for 2)
(ArgumentError)
         from C:\rbtst\tstbloc.rb:6:in `call'
         from C:\rbtst\tstbloc.rb:2:in `tstbloc'
         from C:\rbtst\tstbloc.rb:6

Q2: What exactly is the semantic difference between using a bloc parameter
(with &) and a yield?
e.g. the above code behaves differently (and I expected otherwise :-() after
rewriting it as:

    def tstbloc
        yield 10,20,30
    end

    tstbloc {  |i| puts "got: #{i}"}        # this produces the output as
below
    tstbloc {|i,j| puts "got: #{i}"}        # and this works too!

produces:

    got: 102030
    got: 10

Q3: And what about using Proc?

    def tstproc
       inst = Proc.new
       inst.call 11,22,33
    end

    tstproc {|i| puts "got: #{i}"}
    tstproc {|i,j| puts "got: #{i}"}

produces:
    got: 112233

    C:\rbtst\tstbloc.rb:2: wrong number of arguments (3 for 2)
(ArgumentError)
         from C:\rbtst\tstbloc.rb:6:in `call'
         from C:\rbtst\tstbloc.rb:2:in `tstbloc'
         from C:\rbtst\tstbloc.rb:6

Thanks,
-- Shanko