问题
In Scala, does AnyRef.clone perform a shallow or deep copy?
回答1:
Short answer: shallow.
Not-so-short answer: Unless it's overridden, AnyRef.clone() uses the Java's Object.clone() as its implementation.
Javadoc on Object.clone():
The method clone for class Object performs a specific cloning operation. First, if the class of this object does not implement the interface Cloneable, then a CloneNotSupportedException is thrown. Note that all arrays are considered to implement the interface Cloneable. Otherwise, this method creates a new instance of the class of this object and initializes all its fields with exactly the contents of the corresponding fields of this object, as if by assignment; the contents of the fields are not themselves cloned. Thus, this method performs a "shallow copy" of this object, not a "deep copy" operation.
Please note:
- AnyRef.clone(), like its counterpart in Java, has a "protected" access level, so its not callable from everywhere.
- You will need to implement Cloneable in order for clone() to work.
Long answer: Read Effective Java, 2nd Edition, Item 11: Override clone judiciously
Summary: Don't use it. There are better alternatives.
来源：https://stackoverflow.com/questions/1267261/does-scala-anyref-clone-perform-a-shallow-or-deep-copy