Lua: Booleans

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This article assumes the use of Lua 5.1. Information may not be accurate or may need revision if you are using a different version.

Up until Lua 5.0, Lua did not have an explicit boolean type; instead, boolean operations were performed using nil as false and any other non-nil datatype as true. Lua 5.0 introduced true and false as a true and separate boolean type. When coercion is allowed, non-boolean values will be coerced: nil is seen as false, anything else as true. Only the result of a boolean expression is the returned boolean value.

This is important to remember, as this case shows:

test = 1

if test then 
    print("evaluated true") --> this is printed
else 
    print ("evaluated false") 
end

if test == true then 
    print("evaluated true") 
else 
    print ("evaluated false") --> this is printed
end

If you check the coercion notes, you will see Lua does not automatically coerce values used in boolean comparisons; therefore, the second if statement will evaluate to false. However, the first will evaluate to true, because coercion is allowed in this case.