CODEWITHSUNDEEP
julia
overseas
overseas

Reputation: 1731

Create Julia Tuple

As I am trying to understand metaprogramming in Julia: What is missing in this code, respectively, how can I call the proper constructor of Tuple?

x = (:a, :b)
p = quote
    f_a = 3
    f_b = 4
    y = Tuple($([Symbol("f_", k) for k in x]...))
end

This will generate me the following code:

quote
    f_a = 3
    f_b = 4
    y = Tuple(f_a, f_b)
end

This is of course wrong, because Tuple has no appropriate constructor. I would like to have y being a Tuple in the end, but I don't see yet how to get the additional parentheses.

In other words, what is missing in this code:

x = (:a, :b)

p = quote
    f_a = 3
    f_b = 4
    y = ($([Symbol("f_", k) for k in x]...))
end
eval(p)
@assert isa(y, Tuple)

Upvotes: 1

Views: 199

Answers (1)

carstenbauer
carstenbauer

Reputation: 10127

You can put a comma,

x = (:a, :b)

p = quote
    f_a = 3
    f_b = 4
    y = ($([Symbol("f_", k) for k in x]...),) # added a comma here
end
eval(p)
@assert isa(y, Tuple)

The following might be instructive

julia> (3)
3

julia> (3,)
(3,)

julia> typeof(ans)
Tuple{Int64}

Upvotes: 2

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