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table.unpack with subsequent arguments?
hello, I was using the table.unpack method and I noticed some strange behavior.
01 | function func(supplement, data1, data2) |
02 | print(supplement, data1, data2) |
03 | end |
04 |
05 | local data = { |
06 | "Isaiah", |
07 | "Daniel" |
08 | } |
09 |
10 | func("Camilla", table.unpack(data)) |
11 | -- output: Camilla, Isaiah, Daniel |
notice what happens if I reverse the arguments
1 | function func(data1, data2, supplement) |
2 | print(data1, data2, supplement) |
3 | end |
4 |
5 | -- same data |
6 |
7 | func(table.unpack(data), "Camilla") |
8 | -- output: Isaiah, Camilla, nil |
now this isn't a huge problem because I could even just unpack these into variables first then pass them in. I am wondering if anybody knows why this happens?
1 answer
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1
That's really simple, and it's just basic Lua variadic behaviour. For any function which has multiple returns, it will be reduced to its first term if it is added anywhere but the tail of a tuple.
Consider this
1 | function r2() |
2 | return "a", "b" |
3 | end |
This returns two values, as you'd expect. And, as you'd expect,
1 | print(r2()) --> a, b |
This prints two values. But only if the function is the last in the list.
1 | print(r2(), "c") --> a, c |
2 | print("c", r2()) --> c, a, b |