Add a method to a class at runtime?

ruby-talk
1

module SomeModule
  def happy?
    puts 'yes'
  end
end

# I can do this:
some_object.extend(SomeModule)
some_object.happy? # -> 'yes'

# But I really need to give the class the method (not just instances)
# because I have a collection of hundreds of thousands of objects
# and need them all to have the method quickly.

# The problem is that I don't know the class that needs to include the
method
# until runtime!

# This won't work:

some_object.class.include(SomeModule)
# -> NoMethodError: private method `include' called for <SomeClass>

# What is the workaround to add a method to a class (known only at
runtime)?

Thanks

2

Note to self,
class_eval or module_eval should work

# from ri class_eval:
class Thing
end
a = %q{def hello() "Hello there!" end}
Thing.module_eval(a)
puts Thing.new.hello()
Thing.module_eval("invalid code", "dummy", 123)

3

bwv549 wrote:

module SomeModule
  def happy?
    puts 'yes'
  end
end

# I can do this:
some_object.extend(SomeModule)
some_object.happy? # -> 'yes'

# But I really need to give the class the method (not just instances)
# because I have a collection of hundreds of thousands of objects
# and need them all to have the method quickly.

# The problem is that I don't know the class that needs to include the
method
# until runtime!

# This won't work:

some_object.class.include(SomeModule)
# -> NoMethodError: private method `include' called for <SomeClass>

# What is the workaround to add a method to a class (known only at
runtime)?

Thanks

You have a misunderstanding here. *All* methods are added to classes at
runtime, since that's the only "time" ruby has (there is no compile
time). Of course, C-extensions are excluded from this.
You can always reopen a class:
class Array
  def foo; "foo!"; end
end
.foo # => "foo!"

Regards
Stefan

···

--
Posted via http://www.ruby-forum.com/\.

4

And no need to use strings:
  module Joi
    def happy?; true; end
  end

  class Foo; end

  f1 = Foo.new
  f2 = Foo.new

  f2.class.class_eval{ include Joi }
  p f1.happy?
  #=> true

···

On Aug 30, 12:58 pm, bwv549 <jtpri...@gmail.com> wrote:

# from ri class_eval:
class Thing
end
a = %q{def hello() "Hello there!" end}
Thing.module_eval(a)
puts Thing.new.hello()
Thing.module_eval("invalid code", "dummy", 123)

5

Stefan Rusterholz wrote:

bwv549 wrote:

module SomeModule
  def happy?
    puts 'yes'
  end
end

# I can do this:
some_object.extend(SomeModule)
some_object.happy? # -> 'yes'

# But I really need to give the class the method (not just instances)
# because I have a collection of hundreds of thousands of objects
# and need them all to have the method quickly.

# The problem is that I don't know the class that needs to include the
method
# until runtime!

# This won't work:

some_object.class.include(SomeModule)
# -> NoMethodError: private method `include' called for <SomeClass>

# What is the workaround to add a method to a class (known only at
runtime)?

Thanks

You have a misunderstanding here. *All* methods are added to classes at
runtime, since that's the only "time" ruby has (there is no compile
time). Of course, C-extensions are excluded from this.
You can always reopen a class:
class Array
  def foo; "foo!"; end
end
.foo # => "foo!"

Regards
Stefan

That one went off too early, The missing paragraph:
As for your problem: you can use include, e.g. via
YourClass.send(:include, ModuleName), if you have the classname as
Symbol or String, see Module#const_get.

Regards
Stefan

···

--
Posted via http://www.ruby-forum.com/\.