Editing Eval (section)

=== Ruby ===
The [[Ruby (programming language)|Ruby programming language]] interpreter offers an <code>eval</code> function similar to Python or Perl, and also allows a [[Scope (programming)|scope]], or [[Name binding|binding]], to be specified.

Aside from specifying a function's binding, <code>eval</code> may also be used to evaluate an expression within a specific class definition binding or object instance binding, allowing classes to be extended with new methods specified in strings.

<syntaxhighlight lang="ruby">
a = 1
eval('a + 1') #  (evaluates to 2)

# evaluating within a context
def get_binding(a)
  binding
end
eval('a+1',get_binding(3)) # (evaluates to 4, because 'a' in the context of get_binding is 3)
</syntaxhighlight>

<syntaxhighlight lang="ruby">
class Test; end
Test.class_eval("def hello; return 'hello';end") # add a method 'hello' to this class
Test.new.hello                    # evaluates to "hello"
</syntaxhighlight>