Overriding ENV[]

[Jos Backus]

$ cat x
#!/usr/bin/env ruby
class << ENV
define_method[], lambda { |v| v.upcase })
end
p ENV['FOO']
$ FOO=foo ./x
"FOO"
$

But what if I want to call the original ENV[] inside the new method?

 

[Jesús Gabriel y Galán]

$ cat x
#!/usr/bin/env ruby
class << ENV
=A0define_method[], lambda { |v| v.upcase })
end
p ENV['FOO']
$ FOO=3Dfoo ./x
=A0"FOO"
$

But what if I want to call the original ENV[] inside the new method?

You can use alias_method like this:

irb(main):001:0> a =3D [1,2,3]
=3D> [1, 2, 3]
irb(main):005:0> class << a
irb(main):006:1> alias_method ld, :[]
irb(main):007:1> end
=3D> #<Class:#<Array:0x2932038>>
irb(main):008:0> a.old(0)
=3D> 1
irb(main):009:0> class << a
irb(main):010:1> def [](val)
irb(main):011:2> old(val).to_s.upcase
irb(main):012:2> end
irb(main):013:1> end
=3D> nil
irb(main):014:0> a[0]
=3D> "1"

I tested with an array, but ENV should work too.

 

[Jos Backus]

You can use alias_method like this:

irb(main):001:0> a = [1,2,3]
=> [1, 2, 3]
irb(main):005:0> class << a
irb(main):006:1> alias_method ld, :[]
irb(main):007:1> end
=> #<Class:#<Array:0x2932038>>
irb(main):008:0> a.old(0)
=> 1
irb(main):009:0> class << a
irb(main):010:1> def [](val)
irb(main):011:2> old(val).to_s.upcase
irb(main):012:2> end
irb(main):013:1> end
=> nil
irb(main):014:0> a[0]
=> "1"

I tested with an array, but ENV should work too.

This works, thanks Jesús. I tried

alias_method ld_[], :[]

which produces a syntax error. I should have tried a little harder.