What feature of what language does Clojure Protocols derive from?

Question

Note: this is not a question about "How to Use Protocols"

This is a question about what inspired the idea.

In particular, what I want is to get something like:

XYZ + ABC inspired Clojure Protocols

Then, I can go off and read about directions people went with XYZ and ABC for language features.

Thanks!

Gert · Accepted Answer · 2012-07-16T00:20:38.717

If you know Java, Clojure protocols are similar to Java interfaces - but better. The Clojure website says this about protocols (and there's more background information and rationale about protocols on that page):

Provide a high-performance, dynamic polymorphism construct as an alternative to interfaces

Support the best parts of interfaces

specification only, no implementation

a single type can implement multiple protocols

While avoiding some of the drawbacks

Which interfaces are implemented is a design-time choice of the type author, cannot be extended later (although interface injection might eventually address this)

implementing an interface creates an isa/instanceof type relationship and hierarchy

Avoid the 'expression problem' by allowing independent extension of the set of types, protocols, and implementations of protocols on types, by different parties

do so without wrappers/adapters

Support the 90% case of multimethods (single dispatch on type) while providing higher-level abstraction/organization

Furthermore, you might find Solving the Expression Problem with Clojure 1.2 an interesting read:

Clojure expert Stuart Sierra introduces you to new features in Clojure 1.2 that solve the Expression Problem, a classic programming dilemma. Protocols let you extend preexisting types to new methods, and datatypes let you extend preexisting methods to new types — all without changing the existing code. You'll also see how Java™ interfaces and classes can interact with Clojure protocols and datatypes.

Note that Java interfaces, in turn, are directly taken from Objective-C protocols (Objective-C was *the* main influence on the design of Java). Objective-C protocols, then, are inspired by the idea of protocols in Smalltalk, which in Smalltalk are purely a documentation convention, which Objective-C turned into a language feature. — Jörg W Mittag, May 11 '15 at 22:12

score 3 · Answer 2 · edited May 23 '17 at 12:30

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I don't know, was Clojure Protocols inspired by something, except desire to solve Expression Problem, but Protocols are doing similar thing as Haskell typeclasses, for example...

Look to this question for more information - it also mentions Scala traits

edited May 23 '17 at 12:30

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answered Jul 16 '12 at 06:23

Alex Ott

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What feature of what language does Clojure Protocols derive from?

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