CODEWITHSUNDEEP
lua
lukas.pukenis
lukas.pukenis

Reputation: 13597

Lua unpack() messing arguments

I have this test function which simply prints values passed to it

function test1(...)
  for k, v in ipairs(arg) do
    print(v)    
  end
end

function test2(...)
  for k, v in pairs(arg) do
    print(v)    
  end
end

-- GOOD behavior
test1(1, 2, 3, 4) -- produces 1 2 3 4
test2(1, 2, 3, 4) -- produces 1 2 3 4

-- BAD behavior
test1( unpack({1,2}), 3, 4) -- produces 1 3 4
test2( unpack({1,2}), 3, 4) -- produces 1 3 4 3

Can someone explain this behavior to me ?

Upvotes: 7

Views: 1824

Answers (1)

lhf
lhf

Reputation: 72312

This behavior is not specific to unpack. The Lua Reference Manual says:

"Both function calls and vararg expressions can result in multiple values. If a function call is used as a statement (see §3.3.6), then its return list is adjusted to zero elements, thus discarding all returned values. If an expression is used as the last (or the only) element of a list of expressions, then no adjustment is made (unless the expression is enclosed in parentheses). In all other contexts, Lua adjusts the result list to one element, either discarding all values except the first one or adding a single nil if there are no values."

(my emphasis)

Upvotes: 10

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