Unary expression can be a constant expression

[chiranSachintha]

Description:

following program should be valid

public const int MIN_VALUE = (-(10)); //currently gives error as `expression is not a constant expression`
public const int MAX_VALUE = -(10); //currently gives error as `expression is not a constant expression`
public function main() {
}

[rdhananjaya]

Assigning to RandikaJ