I've some currently some Lua code using the following syntax:
if (foo == nil or foo == '') then
foo = "some default value"
end
The goal of the if condition is to test foo is neither an empty string, neither a nil value.
Can this code be simplified in one if test instead two?
One simple thing you could do is abstract the test inside a function.
local function isempty(s)
return s == nil or s == ''
end
if isempty(foo) then
foo = "default value"
end
Can this code be simplified in one if test instead two?
nil and '' are different values. If you need to test that s is neither, IMO you should just compare against both, because it makes your intent the most clear.
That and a few alternatives, with their generated bytecode:
if not foo or foo == '' then end
GETGLOBAL 0 -1 ; foo
TEST 0 0 0
JMP 3 ; to 7
GETGLOBAL 0 -1 ; foo
EQ 0 0 -2 ; - ""
JMP 0 ; to 7
if foo == nil or foo == '' then end
GETGLOBAL 0 -1 ; foo
EQ 1 0 -2 ; - nil
JMP 3 ; to 7
GETGLOBAL 0 -1 ; foo
EQ 0 0 -3 ; - ""
JMP 0 ; to 7
if (foo or '') == '' then end
GETGLOBAL 0 -1 ; foo
TEST 0 0 1
JMP 1 ; to 5
LOADK 0 -2 ; ""
EQ 0 0 -2 ; - ""
JMP 0 ; to 7
The second is fastest in Lua 5.1 and 5.2 (on my machine anyway), but difference is tiny. I'd go with the first for clarity's sake.
Source: Stackoverflow.com