Why is cloning (in .NET) so difficult?

Question

In the past I had the need to clone objects, only to find that they don't implement a <code>Clone()</code> method, forcing me to do it by hand (create a new instance and copy all properties from the original to the new one). Why isn't cloning as easy as duplicating the memory block the object is allocated in, and thus have the `Clone` method in the <code>object</code> class, having all classes in .NET inherit it?

Answer 1

It is both easier and harder than you might imagine.

What you are referring to, duplicating a memory block, is only a shallow clone.

If an object has references to other object, those other objects also need to be duplicated for the object to be cloned properly.

A deep clone is possible to do automatically, but is very slow (activating a new instance, reflecting and iterating over all fields of the type and recursively cloning any nested objects)

If all you want is to say, be able to copy a small collection of value types, define your type as a 'struct' instead of a 'class', and you will get the ability to easily create clones of an object. Types defined as a 'struct' inherit from 'ValueType', and are passed by value (eg, a duplicate) to functions, or when assigned to fields. Builtin types such as 'int', 'float', 'double' and the like are all value-types, and you can expect your own value-types to behave the same way. If you need 'null' as a value, you must use Nullables (eg, use 'int?' instead of 'int' to allow null to be a possible value)

With a struct/value type, creating a shallow is as easy as assigning some other field/variable to the value you want to copy. Creating a deep copy (unless the type is composed of only value types) still has the same problems as described above.