Каким образом можно реализовать механизм Copy-on-write в собственной реализации?

The Copy-on-write (COW) mechanism allows efficient memory management by delaying data copying until modification. In a custom implementation, it can be done as follows:

1. Store data in a shared object with reference counting.
2. When creating a copy, simply increment the reference count without copying data.
3. When attempting to modify data, check the reference count:
   • If it is greater than 1, create a copy of the data, decrement the count of the old object, and work with the new copy.
   • If it is 1, data can be modified directly.

Example in Swift:

class CowBuffer {
    private class Buffer {
        var data: [Int]
        init(data: [Int]) { self.data = data }
    }

    private var buffer: Buffer

    init(data: [Int]) {
        self.buffer = Buffer(data: data)
    }

    private func ensureUnique() {
        if !isKnownUniquelyReferenced(&buffer) {
            buffer = Buffer(data: buffer.data) // copy data
        }
    }

    func append(_ value: Int) {
        ensureUnique()
        buffer.data.append(value)
    }

    var data: [Int] {
        return buffer.data
    }
}

Here, isKnownUniquelyReferenced checks that the buffer object has only one reference, and if not, a copy is made before modification.