CODEWITHSUNDEEP
lualua-table
codinghands
codinghands

Reputation: 1801

How to 'unpack' table into function arguments

I'm trying to call a function in Lua that accepts multiple 'number' arguments

function addShape(x1, y1, x2, y2 ... xn, yn)

and I have a table of values which I'd like to pass as arguments

values = {1, 1, 2, 2, 3, 3}

Is it possible to dynamically 'unpack' (I'm not sure if this is the right term) these values in the function call? Something like..

object:addShape(table.unpack(values))

Equivalent to calling:

object:addShape(1, 1, 2, 2, 3, 3)

Apologies if this is a totally obvious Lua question, but I can't for the life of me find anything on the topic.

UPDATE

unpack(values) doesn't work either (delving into the method addShape(...) and checking the type of the value passed reveals that unpackis resulting in a single string.

Upvotes: 37

Views: 63743

Answers (3)

HSLM
HSLM

Reputation: 2012

Whoever comes here and has Lua version > 5.1 unpack is moved into the table library so you can use: table.unpack

For more info: https://www.lua.org/manual/5.2/manual.html

Upvotes: 17

Oliver
Oliver

Reputation: 29493

This is not an answer about unpack, but a suggestion to use a different technique. Instead, do 

function object:addShape(values)
    for i,v in ipairs(values) do 
        x,y = v.x, v.y
        ...
    end
end

function getPairs(values)
    xyPairs = {}
    for i=1,#values,2 do 
        v = {x=values[i], y=values[i+i] }
        table.insert(xyPair, v)
    end
    return xyPairs
end

values = {1, 1, 2, 2, 3, 3}
object:addShape(getPairs(values))

The amount of work to be done should be similar as unpacking and the additional processing you will have to do in addShape() to support variable number of named arguments.

Upvotes: -7

John Zwinck
John Zwinck

Reputation: 249153

You want this:

object:addShape(unpack(values))

See also: http://www.lua.org/pil/5.1.html

Here's a complete example:

shape = {
  addShape = function(self, a, b, c)
    print(a)
    print(b)
    print(c)
  end
}

values = {1, 2, 3}
shape:addShape(unpack(values))

Upvotes: 45

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