Accessing array elements in lua does not work well

Question

When I have a function that return multiple values I can either store them in seperat values or use the {} operator to get an array.

To access the values I can either define a variable to store the value or access the array via array[index]. When using a temp var to print the value I code:

function myTest()
  return "abc", "def", "geh";
end

a = {myTest()};
v = a[2];
print(v);

which works very well. But when printing the "indexed array converted return value" from the function with

function myTest2()
  return "abc", "def", "geh";
end

print({myFunction2()}[2]);

nothing gets printed.

Can someone explain me why?

g_bor · Accepted Answer · 2019-09-23 20:57:13Z

3

The form:

{myFunction2()}[2]

is not syntactically valid. I get an unexpected symbol error for that.

You can write it like:

({myFunction2()})[2]

and then it works as expected.

answered Sep 23, 2019 at 20:57

g_bor

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1 Comment

DarkWiiPlayer Over a year ago

note that you can use luac -p <file.lua> to parse a Lua file for syntax errors without executing it (Useful when your workin on a system that silently drops syntax errors)

DarkWiiPlayer · Accepted Answer · 2019-09-25 12:35:48Z

3

Just don't. When you want to immediately access the Nth return value of a function, use (select(N, ...)), which does not create a new table (and thus creates less work for the GC)

function myTest2()
  return "abc", "def", "geh";
end

print( (select(2, myFunction2())) );

Note that enclosing a list of values in () truncates it to the first value; this is necessary because select(N, ...) returns the Nth and all following values. (select(N, ...)) returns only the Nth value.

answered Sep 25, 2019 at 12:35

DarkWiiPlayer

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