Redefining Kernel Methods on the Fly

[Gavin Kistner]

As part of my Quest to find a clean way to get #puts and #print to
'work' in ERB, I was experimenting with ways I thought I could
redefine Kernel methods from within a method. Why don't test1 and
test2 work in the following code?

module Kernel
alias_method :_puts, uts
def puts(s); _puts "HIDDEN"; end
end
puts "1: I DON'T WANNA SEE THIS"
module Kernel
undef_method uts
alias_method uts, :_puts
end
puts "1: OK to see this"

def run_test1
Kernel.instance_eval{
alias_method :_puts, uts
def puts(s); _puts "HIDDEN"; end
}
puts "2: I DON'T WANNA SEE THIS"
Kernel.instance_eval{
undef_method uts
alias_method uts, :_puts
}
puts "2: OK to see this"
end
run_test1

def run_test2
kb = Kernel.instance_eval{ binding }
eval( "alias_method :_puts, uts", kb )
eval( 'def puts(s); _puts "HIDDEN"; end', kb )
puts "3: I DON'T WANNA SEE THIS"
eval( "undef_method uts", kb )
eval( "alias_method uts, :_puts", kb )
puts "3: OK to see this"
end
run_test2

[[Slim:~/Desktop] gavinkis% ruby -vW0 binding_test.rb
ruby 1.8.2 (2004-12-25) [powerpc-darwin8.0.0]
HIDDEN
1: OK to see this
2: I DON'T WANNA SEE THIS
2: OK to see this
HIDDEN
HIDDEN

 

[nobuyoshi nakada]

Hi,

At Fri, 19 Aug 2005 14:50:38 +0900,
Gavin Kistner wrote in [ruby-talk:152854]:

def run_test1
Kernel.instance_eval{

Use module_eval instead of instance_eval.

 

[Gavin Kistner]

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At Fri, 19 Aug 2005 14:50:38 +0900,
Gavin Kistner wrote in [ruby-talk:152854]:

def run_test1
Kernel.instance_eval{

Use module_eval instead of instance_eval.

Er, yup, that did the trick! Silly I didn't think of it.

Any idea why the last item (using eval with the binding of Kernel)
manages to change the puts, but cannot change it back?

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