I am trying to optimize my IF statement in Lua. When there are two conditions in an IF statement with the AND operator, does Lua read left to right and stop as soon as it reaches one false? That is, if there is a condition which is quick to check and a condition which is slower to check, is it more efficient to put the condition which is quick to check first (i.e. left most)?

For example, assume I have two functions that return true or false, quick_fn() and slow_fn(), and I want to execute code only if both functions return true. In terms of speed, is there a difference between the following two ways of writing this code? If Option #1 is equivalent, should I always be putting the quick_fn() in the leftmost spot?

Option #1:

if quick_fn() AND slow_fn() then 
  [code]
end

Option #2:

if quick_fn() then
  if slow_fun() then
    [code]
  end
end

CodePudding user response：

This is explained in the Lua documentation (emphasis added):

The negation operator not always returns false or true. The conjunction operator and returns its first argument if this value is false or nil; otherwise, and returns its second argument. The disjunction operator or returns its first argument if this value is different from nil and false; otherwise, or returns its second argument. Both and and or use short-circuit evaluation; that is, the second operand is evaluated only if necessary.

Note that the operator is spelled and, not AND. Lua is case-sensitive.