Why are objects automatically passed by reference?

Why are objects automatically passed by reference?

They're not.

Is there any particular benefit from forcing the cloning process for them instead of treating objects more like int, double, boolean, etc. in these cases?

There's no "cloning process" for reference types, only for value types.

I think you're confusing different concepts:

• value types vs. reference types

  For value types (such as primitive numeric types, enums, and structures like DateTime), the value of the variable is the object itself. Assigning the variable to another (or passing it as a parameter by value) creates a copy of the object.

  For reference types (such as object, string, classes (not structs) etc), the value of the variable is a reference to the object. Assigning the variable to another (or passing it as a parameter by value) creates a copy of the reference, so it still refers to the same object instance.

• passing parameters by value vs. by reference

  Passing parameters by value means that you pass a copy of the value. Depending on whether it's a value type or reference types, that means a copy of the object itself, or a copy of the reference. If the callee modifies members of a value type passed as a parameter, the caller won't see the changes, since the callee is working on a copy. On the other hand, if the callee modifies members of a reference type passed as a parameter, the caller will see the changes, because the callee and caller both have a reference to the same object instance.

  Passing parameters by reference means that you pass a reference to a variable (which may be a variable of value type or reference type). The value is not copied: it is shared between the caller and the callee. So any change made by the callee (including assignment of a new value to the parameter) will be seen by the caller.

  Unless specified otherwise (with the ref or out keywords), all parameters are passed by value, including reference types. It's just that for reference types, the value that is passed is a reference, but it's still passed by value.

I suggest you read Jon Skeet's article Parameter passing in C# for a better explanation.

All method arguments are passed by value unless you explicitly specify that they should be passed by reference using the ref or out keyword. That means that if you pass a variable to a method parameter then the contents of the variable is copied and passed to the method.

If the variable is a value type, which basically means a struct, then the variable contains an object and so that object is copied. If the variable is a reference type, which basically means a class then the variable contains a reference to an object so that reference is copied.

If you declare a parameter as ref or out then a reference to the variable is created and that is passed to the method. If the variable contains an object then a reference to that object is created and if the variable contains a reference then a reference to that reference is created.