How do I create a method that takes any iterable collection of strings?

Question

I have a function, f. I want to add a method that takes any container of Strings. For example, I want to write a method that generates the following when needed:

f(xs::Array{String, 1}) = ...
f(xs::DataArray{String, 1}) = ...
f(xs::ITERABLE{String}) = ...

Is this possible to do in Julia's type system? Right now, I'm using a macro to write a specialized method when I need it.

@make_f(Array{String, 1})
@make_f(DataArray{String, 1})

This keeps things DRY, but it feels...wrong.

Answer 1

Can't you just use duck typing? I.e., just assume that you're feeding the function an object of the right type and throw an error if at some point e.g. you don't have a string in your iterable.

This should improve once you can really talk about iterables using traits; currently there is no iterable type. Scott's answer, for example, will not work with a tuple of strings, even though that is iterable.

E.g.

julia> f(x) = string(x...)  # just concatenate the strings
f (generic function with 1 method)

julia> f(("a", "á"))
"aá"

julia> f(["a", "á"])
"aá"

julia> f(["a" "b"; "c" "d"])  # a matrix of strings!
"acbd"

Answer 2

At least in Julia 0.4, the following should work:

julia> abstract Iterable{T} <: AbstractVector{T}

julia> f{T<:Union{Vector{String},Iterable{String}}}(xs::T) = 1
f (generic function with 1 method)

julia> x = String["a", "é"]
2-element Array{AbstractString,1}:
 "a"
 "é"

julia> f(x)
1