What does .. (double period) mean in OCaml?

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I'm looking at the following code:

  type (_, _, _) t = ..

and can't find anything about it

1 Answers

It's an extensible variant type.

A variant type that can be extended later on. Copying the example from the doc:

type attr = ..

type attr += Str of string

type attr +=
  | Int of int
  | Float of float
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