Lua Booleans in Lua Emulating Ternary Operator with 'and' 'or' logical operators.
Example
In lua, the logical operators and and or returns one of the operands as the result instead of a boolean result. As a consequence, this mechanism can be exploited to emulate the behavior of the ternary operator despite lua not having a 'real' ternary operator in the language.
Syntax
condition and truthy_expr or falsey_expr
Use in variable assignment/initialization
local drink = (fruit == "apple") and "apple juice" or "water"
Use in table constructor
local menu =
{
meal = vegan and "carrot" or "steak",
drink = vegan and "tea" or "chicken soup"
}
Use as function argument
print(age > 18 and "beer" or "fruit punch")
Use in return statement
function get_gradestring(student)
return student.grade > 60 and "pass" or "fail"
end
Caveat
There are situations where this mechanism doesn't have the desired behavior. Consider this case
local var = true and false or "should not happen"
In a 'real' ternary operator, the expected value of var is false. In lua, however, the and evaluation 'falls through' because the second operand is falsey. As a result var ends up with should not happen instead.
Two possible workarounds to this problem, refactor this expression so the middle operand isn't falsey. eg.
local var = not true and "should not happen" or false
or alternatively, use the classical if then else construct.
