CODEWITHSUNDEEP
functionluatuples
thor
thor

Reputation: 22460

How to pass a tuple as arguments to a Lua function?

Is there a way to pass a tuple as the parameters of a Lua function?

For example, I have a function that returns multiple values

function f(a,b)  return b,a end

and I want this function f to be repeatedly applied, so I can write:

f (f ... f(1,2))

But what if I need to store this initial tuple (1,2) as a variable init?

f (f ... f(init))

Is there support for this?

According to this answer, it seems python has it with the splat operator *.

Upvotes: 6

Views: 21149

Answers (1)

Nicol Bolas
Nicol Bolas

Reputation: 473182

Lua does not have "tuples".

When a function returns multiple values, it returns multiple values. They aren't put together into some data structure; they're separate values. If you want to store multiple return values in a single data structure, you have to actually do that.

Lua 5.2 has the table.pack function, which you can use to store multiple return values in a table. But it does so in such a way that you can decompose them later:

local values = table.pack(f(1, 2))

f(table.unpack(values, values.n))

unpack exists in Lua 5.1, but pack does not. You can emulate it easily enough:

function pack(...)
    return {n = select("#", ...), ...}
end

Upvotes: 12

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