Passing a method block to a parent class

ruby-talk
1

If I have

**** CODE ****

class A
def method1( argument )
yield( argument )
end
end

class B < A
def method1( argument )
puts argument
super.method1( argument )
end
end

obj = B.new
obj.method1( ‘foo’ ) { |arg| puts arg + ‘bar’ }

**** CODE ****

How do I change this to allow class A to get the block. Bascially I
want to override a method to do some pre-processing, but call the
superclass to actually implement the method. The superclass method
uses a block so how do I pass that block to the superclass?

Thanks,

Eric

2

**** CODE ****

class A
def method1( argument )
yield( argument )
end
end

class B < A
def method1( argument )
puts argument
super.method1( argument )

  super   #    <----------------###

end
end

obj = B.new
obj.method1( ‘foo’ ) { |arg| puts arg + ‘bar’ }

**** CODE ****

Thanks,

Eric

Add parameters to super only if you want to
override its default behaviour of passing
all original parameters on.

#-> foo
#-> foobar

daz

···

“Eric Anderson” eric.anderson@sterlingpresence.com wrote:

3

…

def method1( argument )
puts argument
super.method1( argument )
end
end

The above is equivalent to

···

“Eric Anderson” eric.anderson@sterlingpresence.com wrote

class B < A
def method1( argument )
puts argument
super(argument).method1( argument )
end
end

Just write this as

class B < A
def method1( argument )
puts argument
super
end
end

and things will work as you probably intended.
B.t.w this also works if you modify the argument
supplied to super, as in

class A
def mth(s)
yield s
end
end

class B < A
def mth(s)
super(s+‘b’)
end
end

class C < B
def mth(s)
super(s+‘c’)
end
end

C.new.mth(‘a’) {|x| p x + ‘d’ } # => “abcd”

/Christoph

4

To pass blocks around you have to use proc arguments.

If you declare a method thus:

def method2 (argument, &block)
end

Then any block associated with a call to the method will be turned into
a Proc object and assigned to the &-marked parameter (which must be last
in the list). Like *, this works both ways; if you pass a Proc as the
last parameter of a method call and put a & in front of it, the called
method sees it as a block.

So this should do what you want:

class B < A
def method1( argument, &block )
    puts argument
    super.method1( argument, &block )
end
end

-Mark

···

On Sun, Jul 27, 2003 at 07:58:50AM -0700, Eric Anderson wrote:

If I have

**** CODE ****

class A
def method1( argument )
yield( argument )
end
end

class B < A
def method1( argument )
puts argument
super.method1( argument )
end
end

obj = B.new
obj.method1( ‘foo’ ) { |arg| puts arg + ‘bar’ }

**** CODE ****

How do I change this to allow class A to get the block. Bascially I

5

Or more likely:

class B < A
  def method1( argument, &block )
    puts argument
    super( argument, &block )
  end
end

Regards,

Brian.

···

On Wed, Jul 30, 2003 at 11:09:47AM +0900, Mark J. Reed wrote:

If you declare a method thus:

def method2 (argument, &block)
end

Then any block associated with a call to the method will be turned into
a Proc object and assigned to the &-marked parameter (which must be last
in the list). Like *, this works both ways; if you pass a Proc as the
last parameter of a method call and put a & in front of it, the called
method sees it as a block.

So this should do what you want:

class B < A

def method1( argument, &block )
puts argument
super.method1( argument, &block )
end
end