It is acceptable to override standard operators to provide appropriate behaviors for your classes. But it is not appropriate to change those
operators' associativity or precedence from the standard. Doing so will inevitably lead to misuse and mistakes for users of the class.
Instead of overriding an existing operator’s associativity or precedence, you should either let them use the default values or define a completely
new operator.
Noncompliant code example
infix operator - : CustomAdditionPrecedence // Noncompliant. For a different behavior create a different operator
precedencegroup CustomAdditionPrecedence {
associativity: right
}
func - (lhs: MyInt, rhs: MyInt) -> MyInt {
// ...
}
var a = MyInt(10), b = MyInt(5), c = MyInt(5)
print(a - b - c) // against expectations, this outputs 10
Compliant solution
infix operator <- : CustomAdditionPrecedence
precedencegroup CustomAdditionPrecedence {
associativity: right
}
func <- (lhs: MyInt, rhs: MyInt) -> MyInt {
// ...
}
var a = MyInt(10), b = MyInt(5), c = MyInt(5)
var a = MyInt(10), b = MyInt(5), c = MyInt(5)
print(a - b - c) // prints 0 as expected
print(a <- b <- c) // prints 10
