How to use a vector as a type parameter in Julia

This is similar to my previous question , but a little more complex.

Before I was defining a type with an associated integer as a parameter, Intp {p}. Now I would like to define a type using a vector as a parameter.

The following is the closest I can write what I want:

type Extp{g::Vector{T}}


In other words, Extp must be defined relative to a vector, g, and I want the content of c to be another vector whose entries must be of the same type as the g entries.

Well, it won't work.

Problem 1: I don't think I can use :: in the type parameter.

Problem 2: I could get around this by creating types g and c arbitary and just making sure the types in the vectors are the same in the constructor. But, even if I completely select everything and use

type Extp{g}


he doesn't like it anyway. When I try to use it the way I want,

julia> Extp {[1,1,1]} ([0,0,1])

ERROR: type: apply_type: in Extp, expected type {T <: Top}, got array {Int64,1}

So isn't Julia just looking like the specific Vectors associated with types? Does what I am trying to do only work with integers like in my Intp question?

EDIT: In the documentation, I see that type parameters "can be any type at all (or an integer, in fact, although it is explicitly used as a type here)". Does this mean that what I am asking is not possible and that only types and integers work for type parameters? If so, why? (what does integers do this way compared to other types in Julia?)


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2 answers

Here's a relevant quote :

Both abstract and concrete types can be parameterized with other types and some other values ​​(currently integers, characters, bools and tuples).

So your EDIT is correct. An extension of this issue showed up on the Julia issue page (for example # 5102 and # 6081 were two related issues that I found with some discussion), so this may change in the future - I'm guessing not v0.4

. It should be an immutable type that actually makes sense, not Vector

. I'm not sure I understand your application, but does it work Tuple




In Julia 0.4, you can use any "bitstype" as the type parameter. However, the vector is not a bitstring, so this won't work. The closest analogue is using a tuple: for example, it (3.2, 1.5)

is a perfectly valid type parameter.

In a sense, vectors (or any mutable object) are the opposite of types, which cannot change at runtime.



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