Is there any way to express “X is an Int, or a Tuple of X” in Julia? const MyT = Union{Int, NTuple{2, MyT}} fails because MyT is not in scope. I tried the Y-Combinator, but Julia doesn’t like (X{X} where X) either, so it doesn’t seem possible.

I don’t think its possible and probably won’t be.

What are you trying to match? I.e. What is X in the tuple of X?

Let’s say I implement a binary tree using tuples, eg. (1, ((4,5), 3)). How can I define a type which contains all such trees? I could use type/immutable of course, but in my case, that’s inconvenient.

That seems to me like overspecializing the type. If performance is not a concern, I would instead recommend either the simple struct BinaryTree{T} data::Union{T, NTuple{2, BinaryTree{T}}} end or my personal preference abstract BinaryTree{T} struct BinaryNode{T} <: BinaryTree{T} left::Bina…

Note that, in particular, option (2) is the Julia equivalent of algebraic data types available in many languages, which it looks like is what @cstjean is trying to emulate.

Let’s say I implement a binary tree using tuples, eg. (1, ((4,5), 3)). How can I define a type which contains all such trees? I could use type/immutable of course, but in my case, that’s inconvenient. You could also use LightGraphs.jl - they have a specific generator for binary trees.

Thank you for the suggestions everyone, but the binary tree was just an example. My use case is closer to first-order logic. My constants are numbers, tuples of numbers, tuples of tuples of numbers, etc. Not constants: variables, tuples with a variable, tuples of tuples with a variable, etc. A recu…

Perhaps you may then be interested in Nemo.jl , a computer algebra package with long term support and a recent awesome German grant.

Recursive type union

General Usage

dpsanders March 30, 2017, 9:36pm 5

You could make a new type, parametrised by the actual type of the hierarchy of tuples, and then dispatch on the base type.

Topic		Replies	Views
Recursive type? New to Julia	1	1106	October 9, 2018
A unified type of `Tuple` and `Vector` General Usage question , type	4	727	September 21, 2022
Can i declare struct with one type or enother using \|\| New to Julia question	2	472	July 8, 2019
Strange behavior of union of types New to Julia	23	803	March 2, 2023
Transform `Tuple{Union, NonUnion, Union, ...}` to `Union{Tuple{NonUnion, NonUnion, NonUnion, ...}, ...}` General Usage question	4	366	March 5, 2020

Recursive type union

Related topics