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In this Java example, the Printer class has a print method. This print method, rather than performing the print itself, forwards to an object of class RealPrinter. To the outside world it appears that the Printer object is doing the print, but the RealPrinter object is the one actually doing the work.
Go type embedding avoids the need for forwarding methods. [12] Java provides default interface methods since version 8. [4]: 104 Project Lombok [13] supports delegation using the @Delegate annotation on the field, instead of copying and maintaining the names and types of all the methods from the delegated field. [14]
Duck typing is similar to, but distinct from, structural typing.Structural typing is a static typing system that determines type compatibility and equivalence by a type's structure, whereas duck typing is dynamic and determines type compatibility by only that part of a type's structure that is accessed during runtime.
Reportedly, Java inventor James Gosling has spoken against implementation inheritance, stating that he would not include it if he were to redesign Java. [19] Language designs that decouple inheritance from subtyping (interface inheritance) appeared as early as 1990; [ 21 ] a modern example of this is the Go programming language.
With new-style classes, objects and types were unified, allowing the subclassing of types. Even entirely new types can be defined, complete with custom behavior for infix operators. This allows for many radical things to be done syntactically within Python. A new method resolution order for multiple inheritance was also adopted with Python 2.3 ...
If a trait requires the consuming class to provide certain methods, the trait cannot know if those methods are semantically equivalent to the trait's needs. For some dynamic languages, such as Perl, the required method can only be identified by a method name, not a full method signature, making it harder to guarantee that the required method is appropriate.
Function object: with a single method (in C++, the function operator, operator()) it acts much like a function; Immutable object: does not change state after creation; First-class object: can be used without restriction; Container object: contains other objects; Factory object: creates other objects
Inheritance, by contrast, typically targets the type rather than the instances, and is restricted to compile time. On the other hand, inheritance can be statically type-checked, while delegation generally cannot without generics (although a restricted version of delegation can be statically typesafe [7]). Delegation can be termed "run-time ...