CODEWITHSUNDEEP
arraysjuliastrong-typing
TheSorcerer
TheSorcerer

Reputation: 125

Usage of Array of abstract types in Julia

I'm exploring Julia so I'm a newbie. Now I'm exploring its strongly typed features. What I'm realizing is that I can't see the usage of abstract types for arrays. Let me explain with an example:

Let's suppose that I would like to create a function which accepts arrays of reals, no matter its concrete type. I would use:

function f(x::Array{Real})
  # do something
end

This function can be never called without raising a f has no method matching f(::Array{Float64,1})

I would like to call f([1,2,3]) or f([1.,2.,3.]) as long as the type of the element is Real.

I've read that you could promote or convert the array (p.eg f(convert(Array{Real}, [1, 2, 3])) or so) but I see that way really non-dynamic and tedious.

Is there any other alternative rather than getting rid of the strongly typed behaviour?

Thanks.

Upvotes: 6

Views: 3577

Answers (3)

rammelmueller
rammelmueller

Reputation: 1118

Since there's been an updated since the orginal answer, the keyword typealias is gone so that the solution of @Matt B. would now be

const RealArray{T<:Real} = Array{T}
f(x::RealArray) = "do something with $x"

I'll just put this here for the sake of completeness ;)

Upvotes: 4

mrawlik
mrawlik

Reputation: 51

You can do this explicitly using the <: subtype operator:

function f(x::Array)
    return zero.(x)
end

function f(x::Array{<:Real})
    return one.(x)
end

@show f([1, 2])
@show f([1.0, 2.0])
@show f([1im, 2im])

prints

f([1, 2]) = [1, 1]
f([1.0, 2.0]) = [1.0, 1.0]
f([1im, 2im]) = Complex{Int64}[0+0im, 0+0im]

Upvotes: 0

mbauman
mbauman

Reputation: 31342

To expand upon the solution by @user3580870, you can also use a typealias to make the function definition a little more succinct:

typealias RealArray{T<:Real} Array{T}
f(x::RealArray) = "do something with $x"

And then you can use the typealias in anonymous functions, too:

g = (x::RealArray) -> "something else with $x"

Upvotes: 8

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