Check if a string isn t nil or empty in Lua

Question

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

User · Accepted Answer

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

User · Answer

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

[string] Check if a string isn't nil or empty in Lua

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