Take this example Proc:
proc = Proc.new {|x,y,&block| block.call(x,y,self.instance_method)}
It takes two arguments, x and y, and also a block.
I want to execute that block using different values for self. Something like this nearly works:
some_object.instance_exec("x arg", "y arg", &proc)
However that doesn't allow you to pass in a block. This also doesn't work
some_object.instance_exec("x arg", "y arg", another_proc, &proc)
nor does
some_object.instance_exec("x arg", "y arg", &another_proc, &proc)
I'm not sure what else could work here. Is this possible, and if so how do you do it?
Edit: Basically if you can get this rspec file to pass by changing the change_scope_of_proc
method, you have solved my problem.
require 'rspec'
class SomeClass
def instance_method(x)
"Hello #{x}"
end
end
class AnotherClass
def instance_method(x)
"Goodbye #{x}"
end
def make_proc
Proc.new do |x, &block|
instance_method(block.call(x))
end
end
end
def change_scope_of_proc(new_self, proc)
# TODO fix me!!!
proc
end
describe "change_scope_of_proc" do
it "should change the instance method that is called" do
some_class = SomeClass.new
another_class = AnotherClass.new
proc = another_class.make_proc
fixed_proc = change_scope_of_proc(some_class, proc)
result = fixed_proc.call("Wor") do |x|
"#{x}ld"
end
result.should == "Hello World"
end
end
To solve this, you need to re-bind the Proc to the new class.
Here's your solution, leveraging some good code from Rails core_ext:
require 'rspec'
# Same as original post
class SomeClass
def instance_method(x)
"Hello #{x}"
end
end
# Same as original post
class AnotherClass
def instance_method(x)
"Goodbye #{x}"
end
def make_proc
Proc.new do |x, &block|
instance_method(block.call(x))
end
end
end
### SOLUTION ###
# From activesupport lib/active_support/core_ext/kernel/singleton_class.rb
module Kernel
# Returns the object's singleton class.
def singleton_class
class << self
self
end
end unless respond_to?(:singleton_class) # exists in 1.9.2
# class_eval on an object acts like singleton_class.class_eval.
def class_eval(*args, &block)
singleton_class.class_eval(*args, &block)
end
end
# From activesupport lib/active_support/core_ext/proc.rb
class Proc #:nodoc:
def bind(object)
block, time = self, Time.now
object.class_eval do
method_name = "__bind_#{time.to_i}_#{time.usec}"
define_method(method_name, &block)
method = instance_method(method_name)
remove_method(method_name)
method
end.bind(object)
end
end
# Here's the method you requested
def change_scope_of_proc(new_self, proc)
return proc.bind(new_self)
end
# Same as original post
describe "change_scope_of_proc" do
it "should change the instance method that is called" do
some_class = SomeClass.new
another_class = AnotherClass.new
proc = another_class.make_proc
fixed_proc = change_scope_of_proc(some_class, proc)
result = fixed_proc.call("Wor") do |x|
"#{x}ld"
end
result.should == "Hello World"
end
end
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