method

delegate_missing_to

v6.1.7.7 - Show latest stable - 0 notes - Class: Module

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What's this?

delegate_missing_to(target, allow_nil: nil) public

When building decorators, a common pattern may emerge:

class Partition def initialize(event) @event = event end def person detail.person || creator end private def respond_to_missing?(name, include_private = false) @event.respond_to?(name, include_private) end def method_missing(method, *args, &block) @event.send(method, *args, &block) end end

With Module#delegate_missing_to, the above is condensed to:

class Partition delegate_missing_to :@event def initialize(event) @event = event end def person detail.person || creator end end

The target can be anything callable within the object, e.g. instance variables, methods, constants, etc.

The delegated method must be public on the target, otherwise it will raise DelegationError. If you wish to instead return nil, use the :allow_nil option.

The marshal_dump and _dump methods are exempt from delegation due to possible interference when calling Marshal.dump(object), should the delegation target method of object add or remove instance variables.

Show source

# File activesupport/lib/active_support/core_ext/module/delegation.rb, line 295 def delegate_missing_to(target, allow_nil: nil) target = target.to_s target = "self.#{target}" if DELEGATION_RESERVED_METHOD_NAMES.include?(target) module_eval def respond_to_missing?(name, include_private = false) # It may look like an oversight, but we deliberately do not pass # +include_private+, because they do not get delegated. return false if name == :marshal_dump || name == :_dump #{target}.respond_to?(name) || super end def method_missing(method, *args, &block) if #{target}.respond_to?(method) #{target}.public_send(method, *args, &block) else begin super rescue NoMethodError if #{target}.nil? if #{allow_nil == true} nil else raise DelegationError, "\#{method} delegated to #{target}, but #{target} is nil" end else raise end end end end ruby2_keywords(:method_missing) if respond_to?(:ruby2_keywords, true), __FILE__, __LINE__ + 1 end

delegate_missing_to

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