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copied!<p>You can try the following hack:</p> <pre><code>class Proc def call_with_vars(vars, *args) Struct.new(*vars.keys).new(*vars.values).instance_exec(*args, &self) end end </code></pre> <p>To be used like this:</p> <pre><code>irb(main):001:0* lambda { foo }.call_with_vars(:foo => 3) => 3 irb(main):002:0> lambda { |a| foo + a }.call_with_vars({:foo => 3}, 1) => 4 </code></pre> <p>This is not a very general solution, though. It would be better if we could give it <code>Binding</code> instance instead of a Hash and do the following:</p> <pre><code>l = lambda { |a| foo + a } foo = 3 l.call_with_binding(binding, 1) # => 4 </code></pre> <p>Using the following, more complex hack, this exact behaviour can be achieved:</p> <pre><code>class LookupStack def initialize(bindings = []) @bindings = bindings end def method_missing(m, *args) @bindings.reverse_each do |bind| begin method = eval("method(%s)" % m.inspect, bind) rescue NameError else return method.call(*args) end begin value = eval(m.to_s, bind) return value rescue NameError end end raise NoMethodError end def push_binding(bind) @bindings.push bind end def push_instance(obj) @bindings.push obj.instance_eval { binding } end def push_hash(vars) push_instance Struct.new(*vars.keys).new(*vars.values) end def run_proc(p, *args) instance_exec(*args, &p) end end class Proc def call_with_binding(bind, *args) LookupStack.new([bind]).run_proc(self, *args) end end </code></pre> <p>Basically we define ourselves a manual name lookup stack and <code>instance_exec</code> our proc against it. This is a very flexible mechanism. It not only enables the implementation of <code>call_with_binding</code>, it can also be used to build up much more complex lookup chains:</p> <pre><code>l = lambda { |a| local + func(2) + some_method(1) + var + a } local = 1 def func(x) x end class Foo < Struct.new(:add) def some_method(x) x + add end end stack = LookupStack.new stack.push_binding(binding) stack.push_instance(Foo.new(2)) stack.push_hash(:var => 4) p stack.run_proc(l, 5) </code></pre> <p>This prints 15, as expected :)</p> <p><strong>UPDATE:</strong> Code is now also available <a href="https://github.com/niklasb/ruby-dynamic-binding" rel="noreferrer">at Github</a>. I use this for one my projects too now.</p>

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