mixins - What is the difference between 'include' and 'prepend' in Ruby? -
from module
module#append_features(mod) → mod => when module included in another, ruby calls append_features in module, passing receiving module in mod. ruby’s default implementation to add constants, methods, , module variables of module mod if module has not been added mod or 1 of ancestors.
module#prepend_features(mod) → mod => when module prepended in another, ruby calls prepend_features in module, passing receiving module in mod. ruby’s default implementation to overlay constants, methods, , module variables of module mod if module has not been added mod or 1 of ancestors.
can me understand below questions:
what more features of
moduledefinedappend,prependexcept default?how differ functionally?
when use
append_features, whenprepend_features?what difference between 2 bold lines above?
- what features of module defined append , prepend?
as specified in text quoted:
the constants, methods, , module variables
- how differ functionally?
both add methods of mixed-in module passed module (class). difference in lookup order of these methods, in case target class has them defined:
include behaves if target class inherited mixed-in module:
module foobar def puts "2 - module" end end class foo include foobar def puts "1 - implementing class" super end end foo.new.say # => # 1 - implementing class # 2 - module prepend makes methods mixed in module "stronger" , executes them first:
module foobar def puts "2 - module" super end end class foo prepend foobar def puts "1 - implementing class" end end foo.new.say # => # 2 - module # 1 - implementing class the example kindly ripped off here: http://blog.crowdint.com/2012/11/05/3-killer-features-that-are-coming-on-ruby-2-0.html
- when use append_features , when prepend_features?
use prepend when want keep methods of target module (class) @ end of method lookup chain.
some real-world examples can found searching ruby, module , prepend:
- overriding method defined in module
- when monkey patching method, can call overridden method new implementation?
- ruby: module, mixins , blocks confusing?
(note: mentioning methods, easiest picture when comes inheritance , mixing-in, same applies other features.)
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