Question

How is Proc#== evaluated? RDoc says:

prc == other_proc → true or false

Returns true if prc is the same object as other_proc, or if they are both procs with the same body.

But it is not clear what counts as having "the same body". One condition seems to be that the arity must be the same:

->{} == ->{} # => true
->{} == ->x{} # => false
->x{} == ->x{} # => true
->x{} == ->y{} # => true
->x{} == ->y,z{} # => false

But there is more than that. As RDoc says, the body matters:

->{nil} == ->{nil} # => true
->{nil} == ->{false} # => false
->{false} == ->{false} # => true

But at the same time, it looks like the proc is not fully evaluated:

->{} == ->{nil} # => false
->{false} == ->{1 == 2} # => false

To what extent is the body evaluated?

Answer 1

This has changed in Ruby 2.0, so you should not try to compare Procs. They won’t be == unless they are exactly the same object.

The discussion can be found here.

If you really need to compare the code of two blocks and are using MRI, you can play around with RubyVM::InstructionSequence.disassemble(block), or even better in Ruby 2.0 RubyVM::InstructionSequence.of(block).