Performance of calling a function, passing multiple return values from another function call?

Question

A function f() returns multiple values, which are to be fed into a second function g(). I cannot change f(), but I can change g() and all calls to it. I'm wondering if it's possible to say which variant performs best? What does it depend on?

Function header with one table argument
```
function g(arg)
--code
end
```
and function call with table constructor
```
g({f()})
```
Function header with variable number of arguments
```
function g(...)
--code
end
```
and regular function call
```
g(f())
```
Function header with multiple variables (assuming number of f() return values is known)
```
function g(x, y, z)
--code
end
```
and regular function call
```
g(f())
```
A completely different variant?

Judging by later Lua versions, I would expect the table argument to be the slowest (it requires first moving the vararg from the stack to a table on the heap; note also that this is lossy in case of trailing nils), the variadic function to be the second slowest, and the function with the known number of arguments to be the fastest (it requires keeping track of vararg info, such as length). But measure. — Luatic
– Luatic, Commented Aug 13, 2024 at 0:32

Matt · Accepted Answer · 2024-08-13 13:13:20Z

1

First of all, beware of premature optimization. If g(f()) calls are relatively infrequent then the difference might be negligible.

Next, creating an extra table takes time, so option (1) is always slower than (3).

Concerning option (2), it really depends on what g() actually does with the arguments. local args = {...} is an equivalent of option (1), while local x, y, z = ... is the same as (3).

answered Aug 13, 2024 at 13:13

Matt

15.4k1 gold badge25 silver badges31 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Performance of calling a function, passing multiple return values from another function call?

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related