duck-typing

Please, use the right terms for “typing”…

Names matter. That’s one of the things that I learned, working multiple years on programming software. When you have something called “integration”, for example, that means different things for different people, that’s a recipe for disaster.

That’s why I get quite triggered when people use Untyped / Typed, Weak / Strong typed, Uni / Multi typed, to describe programming languages – because it means different things to different people, or are simply wrong. So let’s dive into it:

Untyped languages or languages without types are quite rare: Assembly is the most interesting example (there’s literally no types in Assembly: everything is a memory address, byte, word, etc). Some virtual machines’ bytecodes are also untyped. In this case, most languages are typed. Ruby, for example, have types, and you can dispatch different behavior depending on the type of the caller (because it’s a class-based object-oriented language). Clojure is also typed, because you can do type-based polymorphism with protocols using defprotocol and defrecord for example. You can also use deftype, and if there’s a specific command to define types, how can we call it “untyped”?

Weak / Strong typed is a term that’s hard to define. Some people say that it’s when you have pointers, because you can bypass the typing at all; others, when the compiler erases typing at run-time; some say that’s when the language tries to coerce and implicitly convert from one type to another, to try to figure out what you want…

Now, a language that allows you to bypass typing because you have pointers is called “memory unsafe”; if the compiler erases typing information, is called “type erasure”; coercion of course is called “coercion”, and can be “automatic” or “manual” coercion (for example, most languages try to coerce integers to decimals at some point); even the ability to convert between types is controversial: on Ruby and Scala, operators are also methods of the class (and, on Ruby, you can rewrite methods on classes that already exist, so automatic conversion is a user-defined feature) – so, please use the right term.

Unityped means a language that only have one type. I believe only some markup languages enter on this classification. Calling a language that have multiple types as unityped because someone imagined that all these multiple types can somewhat collapse into a single one is, at minimum, strange; and also, again, we do have a term for languages like Javascript, Ruby, Python, Smalltalk, and Clojure.
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By Maurício Szabo, ago

Em Patópolis, Programe como os Patos

Este é um post sobre “Duck Typing”, e finalmente eu escrevi ele (estava enrrolando para fazê-lo). Acho esse post bem importante porque eu percebi, com a experiência em Ruby, que poucas pessoas sabem lidar com o dinamismo da linguagem (e aproveitá-la ao máximo).

Então, vamos falar um pouco sobre Duck Typing. O básico, a maioria já sabe:

def imprimir(objeto)
  print objeto.falar
end

Ou seja, na declaração do método eu não defino nenhuma regra do que aquele objeto pode receber; apenas chamo os métodos que eu o objeto passado como parâmetro deveria implementar, e confio que vai dar certo. Parece simples, e até um pouco inseguro, então tem gente que prefere fazer umas checagens antes (tipo usando objeto.is_a?(Pessoa) ou objeto.respond_to?(:falar)), mas eu acho que isso quebra a idéia de Duck Typing. Para mim, tudo se resume a uma palavra: Protocolo.

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By Maurício Szabo, ago