Primitive type aliases do not always work due to meta data evaluation

Question

Primitive alias do not work when the meta data is evaluated, for example in the case of def.

In this example, char is interpreted to be the function char rather than the type alias. This is because clojure.lang.Compiler$DefExpr$Parser.parse evaluates the meta data on the symbol.

(def ^char x \space) (String/valueOf x) => CompilerException java.lang.IllegalArgumentException: Unable to resolve classname: clojure.core$char@7b82f7d1

Instead, this has to be written as

(def ^Character/TYPE x \space)

However, when using primitive type hints in-line, they work fine:

(def x \space) (String/valueOf ^char x)

Primitive type aliases should be handled consistently.

Googling shows that this seems to be a well-known problem, but I have not found a Jira issue for it.

Answer 1

Comment made by: alexmiller

Var meta is evaluated. Meta on function signatures and other locations is not. Those two things are that way for historical reasons but would at this point be breaking changes if we changed either of them, so they are not going to change.

One thing that could potentially be done is to detect this particular problem when it happens and create a warning or error. In particular, this would present as a var whose meta :tag is a function.

So, if you want to re-write this ticket as a request for error message, that is something worth considering.

Answer 2

Reference: https://clojure.atlassian.net/browse/CLJ-2072 (reported by alex+import)