Override getter for Kotlin data class

Question

Given the following Kotlin class:

data class Test(val value: Int)

How would I override the Int getter so that it returns 0 if

Answer 1

I found the following to be the best approach to achieve what you need without breaking equals and hashCode:

data class TestData(private var _value: Int) {
    init {
        _value = if (_value < 0) 0 else _value
    }

    val value: Int
        get() = _value
}

// Test value
assert(1 == TestData(1).value)
assert(0 == TestData(-1).value)
assert(0 == TestData(0).value)

// Test copy()
assert(0 == TestData(-1).copy().value)
assert(0 == TestData(1).copy(-1).value)
assert(1 == TestData(-1).copy(1).value)

// Test toString()
assert("TestData(_value=1)" == TestData(1).toString())
assert("TestData(_value=0)" == TestData(-1).toString())
assert("TestData(_value=0)" == TestData(0).toString())
assert(TestData(0).toString() == TestData(-1).toString())

// Test equals
assert(TestData(0) == TestData(-1))
assert(TestData(0) == TestData(-1).copy())
assert(TestData(0) == TestData(1).copy(-1))
assert(TestData(1) == TestData(-1).copy(1))

// Test hashCode()
assert(TestData(0).hashCode() == TestData(-1).hashCode())
assert(TestData(1).hashCode() != TestData(-1).hashCode())

However,

First, note that _value is var, not val, but on the other hand, since it's private and data classes cannot be inherited from, it's fairly easy to make sure that it is not modified within the class.

Second, toString() produces a slightly different result than it would if _value was named value, but it's consistent and TestData(0).toString() == TestData(-1).toString().