The Book of Ruby

Bindings

The eval method may take an optional “binding” argument that, if provided, causes the evaluation to be done within a specific scope or “context.” It probably won’t come as any surprise to discover that, in Ruby, a binding is an object that is an instance of the Binding class. You can return a binding using the binding method. The documentation of eval in the Ruby class library provides this example:

binding.rb

def getBinding(str)
    return binding()
end
str = "hello"
puts( eval( "str + ' Fred'" ) )                    #=> "hello Fred"
puts( eval( "str + ' Fred'", getBinding("bye") ) ) #=> "bye Fred"

Simple as it may look, this example may take a bit of thinking about in order to understand what’s going on. Essentially, the first call to puts evaluates str in the ...