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> In C/C++ I would write !!condition. In  Lua "not not condition" ?

I'm not sure how the ! operation is exactly defined in C(++)
standards, is the result guaranteed to be 1(true) and 0(false) or just
the usual 0 in case of false, or anything else in case of true. If it
is the second, you gain nothing by !!. In C I'd write (condition ? 1 :
0); if I want to fix true to 1, or (condition ? true : false) in C++.

Additionally I challenge "not not" to be a more elegant solution, yes
it is shorter, but the usual reader/debugger that is not you has a
"WTF moment", when reading it, requiring additional parsing/puzzeling,
while if condition then x = true else x = false; is straight easy.

If for "complex condition" you do not rely on Luas unfortunate
condition of having 2 false values, nil or false, but just test for
anything to be not nil, just write ~= nil into the condition, it comes
clear what you mean and the result is defined to be true or false.