Module: LocalEval::ObjectExtensions

Included in:
Object
Defined in:
lib/local_eval.rb

Instance Method Summary collapse

Instance Method Details

#capture { ... } ⇒ Object Also known as: __capture__

Since ‘local_eval` does not alter the `self` inside a block, all methods with an implied receiver will be invoked with respect to this self. This means that all mutator methods defined on the receiver will modify state on the block’s self rather than on the receiver’s self. This is unlikely to be the desired behaviour; and so using the ‘capture` method we can redirect the method lookup to the actual receiver. All code captured by the `capture` block will be `instance_eval`’d against the actual receiver of the method.

Examples:

class C
  def self.hello() @hello end
  def self.capture_test

    # this code will be run against C
    capture { @hello = :captured }

    # this code will be run against the block context
    @goodbye = :goobye
  end
end

C.local_eval { capture_test }
C.hello #=> :captured
@goodbye #=> :goodbye

Yields:

  • The block to be evaluated in the receiver’s context.

Returns:

  • The return value of the block.



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# File 'lib/local_eval.rb', line 94

def capture(&block)
  
  # 1. Get name of enclosing method (method that invoked
  # `capture ` block)
  # 2. Find owner of enclosing method (owner is guaranteed to be
  # a singleton class)
  # 4. Find associated object (attached object) of the singleton class
  # 5. This object will be the receiver of the method call, so
  # instance_eval on it.
  method_name = eval('__method__', block.binding)
  method_owner = method(method_name).owner
  attached_object = method_owner.__attached__
  attached_object.instance_eval &block
end

#local_eval { ... } ⇒ Object

Performs a ‘local_eval` on the block with respect to the receiver. `local_eval` has some advantages over `instance_eval` in that it does not change `self`. Instead, the functionality in the block context is supplemented by the functionality in the receiver.

Examples:

local ivars can be looked up

class C
  def hello(name)
    "hello #{name}!"
  end
end

o = C.new

@name = "John"
o.local_eval { hello(@name) } #=> "hello John!"

Yields:

  • The block to ‘local_eval`

Returns:

  • The return value of the block



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# File 'lib/local_eval.rb', line 63

def local_eval(&block)
  local_eval_with(&block)
end

#local_eval_with(*objs, &block) ⇒ Object

A more general version of ‘local_eval`. `local_eval_with` allows you to inject arbitrary functionality from any number of objects into the block.

Examples:

class A; def self.a; puts "a"; end; end
class B; def self.b; puts "b"; end; end
class C; def self.c; puts "c"; end; end
local_eval_with(A, B, C) { a; b; c }
#=> "a"
#=> "b"
#=> "c"

Parameters:

  • objs (Array) —

    The objects to provide functionality to the block

Returns:

  • The value of the block



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# File 'lib/local_eval.rb', line 24

def local_eval_with(*objs, &block)
  raise "need a block" if !block_given?
  
  objs = Array(self) if objs.empty?
  context = eval('self', block.binding)

  # if the receiver is the same as the block context then don't
  # mix in anything, as functionality is already present.
  if objs.include?(context)
    objs.delete(context)
    return yield if objs.empty?
  end

  # add functionality to anonymous module to ease mixing and unmixing
  functionality = Module.new.gen_include *objs.map { |o| o.is_a?(Module) ? o.singleton_class : o }
  
  # mix the anonymous module into the block context
  context.temp_extend functionality, &block
end