CODEWITHSUNDEEP
clojure
Rafael Custódio
Rafael Custódio

Reputation: 73

What is the difference between these type hinting forms and why is when implemented as an if statement?

I'm new in clojure so I would like to know some things

There are 2 ways to typehint your code, I would like to know the difference

^String and others using #^String

When I saw the code from when I was a little disappointed, it's an if if that is not true could explain me why (assert is a when with throw)

(defmacro when
  "Evaluates test. If logical true, evaluates body in an implicit do."
  {:added "1.0"}
  [test & body]
  (list 'if test (cons 'do body)))

Upvotes: 2

Views: 87

Answers (1)

Carcigenicate
Carcigenicate

Reputation: 45736

  1. #^ is the old, deprecated syntax. Just use ^ now going forward, unless you're running a very old version of Clojure (pre-1.2).

  2. Why be disappointed? This is part of the beauty of languages like Clojure! when is just defined in terms of if. It looks like a language construct, but it's actually just a macro that anyone can write. when literally turns into an if with a do at compile time. It would arguably complicate the language to have made when a special form when it's entirely possible to define it in terms of existing forms.

    The purpose of when is to carry out side effects when the condition holds, but do nothing otherwise. It's simply a readability helper. It's similar to the if-not, and when-not macros that just turn into ifs with their condition negated. They aren't necessary by any means, but they certainly help clean up code.

Upvotes: 7

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