Two modules Foo and Baa respectively define a method with the same name name, and I did include Foo and include Baa in a particular context.
When I call name, how can I disambiguate whether to call the name method of Foo or Baa?
Only the order of modules inclusion decides which one will get called. Can't have both with the same name - the latter will override the former.
Of course, you can do any tricks, just from the top of my head:
module A
def foo
:foo_from_A
end
end
module B
def foo
:foo_from_B
end
end
class C
def initialize(from)
#from = from
end
def foo
from.instance_method(__method__).bind(self).call
end
private
attr_reader :from
end
C.new(A).foo #=> :a_from_A
C.new(B).foo #=> :a_from_B
But that's no good for real life use cases :)
Technically, there is no name collision because the method foo is redefined.
In the following exemple, A.foo is redefined and is never called
module A
def foo
raise "I'm never called"
end
end
module B
def foo
puts :foo_from_B
end
end
class C
include A
include B
end
C.new.foo
# =>
# foo_from_B
If you write A and B module, you can use super to call previous definition of foo. As if it where an inherited method.
module A
def foo
puts :foo_from_A
end
end
module B
def foo
super
puts :foo_from_B
end
end
class C
include A
include B
end
C.new.foo
# =>
# foo_from_A
# foo_from_B
There are side effects and I would not use this but this is doing the trick :
module A
def foo
puts :foo_from_A
end
end
module B
def foo
puts :foo_from_B
end
end
class C
def self.include_with_suffix(m, suffix)
m.instance_methods.each do |method_name|
define_method("#{method_name}#{suffix}", m.instance_method(method_name))
end
end
include_with_suffix A, "_from_A"
include_with_suffix B, "_from_B"
end
c= C.new
c.foo_from_A
c.foo_from_B
begin
c.foo
rescue NoMethodError
puts "foo is not defined"
end
# =>
# foo_from_A
# foo_from_B
# foo is not defined
Provided none of the methods of Foo or Baa call name (which seems a reasonable assumption), one can simply create aliases.
module Foo
def name; "Foo#name"; end
end
module Baa
def name; "Baa#name"; end
end
class C
include Foo
alias :foo_name :name
include Baa
alias :baa_name :name
undef_method :name
end
c = C.new
c.foo_name
#=> "Foo#name"
c.baa_name
#=> "Baa#name"
C.instance_methods & [:foo_name, :baa_name, :name]
#=> [:foo_name, :baa_name]
The keyword alias is documented here. One may alternatively use the method #alias_method. See this blog for a comparison of the two.
Module#undef_method is not strictly necessary. It's just to ensure that an exception is raised if name is called.
You should definetely read about method lookups.
Anyway, I would do it this way:
module Foo
def name
:foo
end
end
module Bar
def name
:bar
end
end
class MyClass
include Foo
include Bar
def foo_name
Foo.instance_method(:name).bind(self).call
end
def bar_name
Bar.instance_method(:name).bind(self).call
end
#
# or even like this: obj.name(Foo)
#
def name(mod)
mod.instance_method(:name).bind(self).call
end
end
BTW if you are using Module#instance_method and UnboundMethod#bind you don't really need to include specific module. This code works:
Foo.instance_method(:name).bind('any object (e.g. string)').call
Related
I'm trying to modify existing ruby code, and ruby is not my first languange. Part of the code is like below:
#someFile1.rb
module A
module B
def somefunction()
end
end
end
class X::Y
include A::B
end
#someFile2.rb
module A
module C
def anotherfunction()
#somefunction() <-- error
end
end
end
class X::Y
include A::C
end
Somehow I can't access method somefunction() in anotherfunction.
How to access method defined in module B in method inside module C? Why it's not working?
Instance methods in modules aren't generally accessible until you mix them into a class and create an object of that class.
module A
module B
def some_method
"foo"
end
end
end
module A
module C
def another_method
some_method
end
end
end
class X
include A::B
include A::C
end
X.new.another_method
# => "foo"
But I'd say it isn't very elegant to have a module that depends upon the fact that some other module has also been mixed into the same object
Class methods in modules, on the other hand, are accessible like this:
module A
module B
def self.somefunction
"foo"
end
end
end
module A
module C
def self.another_function
A::B.somefunction
end
end
end
A::C.another_function
# => "foo"
Assuming you want to call the module functions themselves, you would first need to make them module functions (think static in Java or namespace in C++). Then you can use the :: (namespace resolution) operator. See foo and bar.
If you want to import them into classes, just import both, and both will be visible. See baz and qux.
module A
module B
def self.foo
puts "foo"
end
def baz
puts "baz"
end
end
end
module A
module C
def self.bar
puts "bar"
A::B::foo
end
def qux
puts "qux"
baz
end
end
end
class X
include A::B
include A::C
end
A::C::bar
x = X.new
x.qux
Output:
bar
foo
baz
qux
I have the following code:
module A
def self.included(base)
base.extend(ClassMethods)
end
def foo
a = bar
puts a
end
def bar(str="qwe")
str
end
module ClassMethods
end
end
class B
include A
def bar(str="rty")
str
end
end
B.new.foo #=> "rty"
I wish class B to look like this:
class B
include A
bar "rty"
end
B.new.foo #=> rty
or
class B
include A
HelperOptions.bar "rty" # HelperOptions class should be in module A
end
B.new.foo #=> rty
I tried using define_method, class_eval, and initialize. How can be implemented syntax bar 'rty' or HelperOptions.bar 'rty' and what shall be done in module A?
If I got your question properly you want to define a class method A.bar that defines an instance method B#bar that returns it's argument, you can do it like this:
module A
def self.included(base)
base.extend(ClassMethods)
end
def foo
puts bar
end
module ClassMethods
def bar(str)
define_method(:bar) { str }
end
end
end
class B
include A
bar 'rty'
end
B.new.bar
# => "rty"
B.new.foo
# Output: rty
I am trying to define some classes in Ruby that have an inheritance hierarchy, but I want to use one of the methods in the base class in the derived class. The twist is that I don't want to call the exact method I'm in, I want to call a different one. The following doesn't work, but it's what I want to do (basically).
class A
def foo
puts 'A::foo'
end
end
class B < A
def foo
puts 'B::foo'
end
def bar
super.foo
end
end
Probably, this is what you want?
class A
def foo
puts 'A::foo'
end
end
class B < A
alias bar :foo
def foo
puts 'B::foo'
end
end
B.new.foo # => B::foo
B.new.bar # => A::foo
A more general solution.
class A
def foo
puts "A::foo"
end
end
class B < A
def foo
puts "B::foo"
end
def bar
# slightly oddly ancestors includes the class itself
puts self.class.ancestors[1].instance_method(:foo).bind(self).call
end
end
B.new.foo # => B::foo
B.new.bar # => A::foo
I want to override a method from a module A from another module B that will monkey-patch A.
http://codepad.org/LPMCuszt
module A
def foo; puts 'A' end
end
module B
def foo; puts 'B'; super; end
end
A.module_eval { include B } # why no override ???
class C
include A
end
# must print 'A B', but only prints 'A' :(
C.new.foo
module A
def foo
puts 'A'
end
end
module B
def foo
puts 'B'
super
end
end
include A # you need to include module A before you can override method
A.module_eval { include B }
class C
include A
end
C.new.foo # => B A
Including a module places it above the module/class that is including it in the class hierarchy. In other words, A#foo is not super of B#foo but rather the other way round.
If you think of including a module as a way of doing multiple inheritance this makes sense, include SomeModule is a way of saying, "Treat SomeModule like it is a parent class for me".
To get the output you wanted you need to reverse the inclusion so that B includes A:
module A
def foo; puts 'A' end
end
module B
def foo; puts 'B'; super; end
end
B.module_eval { include A } # Reversing the inclusion
class C
include B # not include A
end
puts C.new.foo
Edit in response to comment:
Then either include both A and B in C with B included after A:
# A and B as before without including B in A.
class C
include A
include B
end
or patch A in C itself and don't bother with B.
# A as before, no B.
class C
include A
def foo; puts 'B'; super; end
end
The only way for this to work is if the method lookup on C is C -> B -> A and there is no way to do this without including B into C.
This is also one solution to your question. I am trying to achieve with module hooks included. When you include the module A into class C. included callbacks defined in module A is called and executed. We included the module B on-fly. So our module A method foo is overridden by Module B foo to print the superclass module method just called super.
module A
def self.included klass
klass.send(:include, B)
end
def foo
puts 'A'
end
end
module B
def foo
super
puts 'B'
end
end
class C
include A
end
C.new.foo #out put A,B
Another way to accomplish this is to include module B when module A is included.
module A
def foo
puts "this should never be called!"
"a"
end
end
module B
def foo
"b"
end
end
module A
def self.included(base)
base.class_eval do
include B
end
end
end
class C
include A
end
C.new.foo # "b"
I'm looking for a way of making a method "personal" - note NOT PRIVATE to a class
here is an example - by "personal" I mean the behaviour of method "foo"
class A
def foo
"foo"
end
end
class B < A
def foo
"bar"
end
end
class C < B
end
a=A.new; b=B.new;c=C.new
I'm looking for a way of producing the following behaviour
a.foo #=> "foo"
b.foo #=> "bar"
c.foo #=> "foo" (ultimate base class method called)
Instead of creating 'personal' methods, change your inheritance structure.
It appears that you want the C class to have only some of the same functionality of the B class while not making changes to the A class.
class A
def foo
"foo"
end
end
class BnC < A
end
class B < BnC
def foo
"bar"
end
end
class C < BnC
end
a=A.new; b=B.new;c=C.new
There's no standard way of doing this. It circumvents how inheritance works. You could implement B's method to do the logic like this:
def foo
instance_of?(B) ? "bar" : super
end
And you could of course define a method on Class that would do this for you similar to public and private.
class Class
def personal(*syms)
special_class = self
syms.each do |sym|
orig = instance_method(sym)
define_method(sym) {|*args| instance_of?(special_class) ? orig.bind(self).call(*args) : super}
end
end
end
Then you can personal :foo in B just like you'd private :foo.
(This isn't at all optimized and I didn't implement the zero-argument behavior that public and private have because frankly it's a huge PITA to do right and even then it's a hack.)
Seems like it could be confusing, but here's one option:
class A
def foo
"foo"
end
end
class B < A
def initialize #when constructing, add the new foo method to each instance
def self.foo
"bar"
end
end
end
class C < B
def initialize #when constructing, do nothing
end
end
More generally, using a similar approach, you can always add a method to a given instance, which of course has no effect on inherited classes or indeed on other instances of the same class.
If you give us specifics of what you're ultimately trying to accomplish we can probably be more helpful.
Answering this is a bit tricky since I don't really see what you want to accomplish in practice, but you could try something like
class C < B
def foo
self.class.ancestors[-3].instance_method(:foo).bind(self).call
end
end
(The ancestors[-3] assumes that A inherits from Object and Kernel and your intent was to access the method from the topmost non-builtin class. Of course you could substitute self.class.ancestors[-3] with just A, or figure out the class from the Array ancestors yourself, etc.)
In practice it would be simpler to alias the original in class B if you can modify it (i.e. alias :foo_from_A :foo in class B < A before the new def foo, then you can call foo_from_A in C). Or just redefine what you want in C. Or design the whole class hierarchy differently.
You can write a shortcut function to handle personalizing methods.
def personalize(*methodNames)
old_init = instance_method(:initialize)
klass = self
modul = Module.new {
methodNames.each { |m|
define_method(m, klass.instance_method(m)) if klass.method_defined?(m)
}
}
methodNames.each { |m|
remove_method(m) if method_defined?(m)
}
define_method(:initialize) { |*args|
# I don't like having to check instance_of?, but this is the only way I
# could thing of preventing the extension of child classes. At least it only
# has to happen once, during initialization.
extend modul if instance_of?(klass)
old_init.bind(self).call(*args)
}
self
end
class A
def foo
"foo"
end
end
class B < A
def foo
"bar"
end
def bam
'bug-AWWK!'
end
personalize :foo, :bam, :nometh
end
class C < B
end
a=A.new; b=B.new; c=C.new
a.foo #=> "foo"
b.foo #=> "bar"
b.bam #=> "bug-AWWK!"
c.foo #=> "foo"
C.instance_method(:foo) # => #<UnboundMethod: C(A)#foo>
c.bam #throws NoMethodError
Sometimes you don't really want an "is a" (inheritance) relationship. Sometimes what you want is "quacks like a." Sharing code among "quacks like a" classes is easily done by using modules to "mix in" methods:
#!/usr/bin/ruby1.8
module BasicFoo
def foo
"foo"
end
end
class A
include BasicFoo
end
class B
def foo
"bar"
end
end
class C
include BasicFoo
end
p A.new.foo # => "foo"
p B.new.foo # => "bar"
p C.new.foo # => "foo"