System.Object 的概念可以被接口取代，通常，所有类都实现了在这个问题上多次提到的想法。虽然我认为这个想法是有效的，但最后我会说它不会给你带来任何东西。即使存在这样的接口，编译器如何确保类实现这些接口的问题仍然存在。
下面是一些示例代码，我在其中尝试探索没有 System.Object 类型的假设情况，以及底层实现以及这些接口的使用情况。
// let's start off by defining interfaces to describe the various methods that are currently available from the System.Object class
public interface IEquatable
{
bool Equals(IEquatable other);
}
public interface IHashCodeGenerator
{
int GetHashCode();
}
public interface ITypeIdentifiable
{
Type GetType();
}
public interface IConvertibleToString
{
string ToString();
}
// This guy throws a wrench into things, because we can't privately (or "protectedly") implement an interface.
// This is discussed further below on the MyClass.MemberwiseClone method.
public interface IMemberwiseCloneable
{
}
// This class simply encapsulates similar functionality found within the System.Object class
public static class ClrInternals
{
[MethodImpl(MethodImplOptions.InternalCall)]
internal static extern bool Equals(IEquatable objA, IEquatable objB);
[MethodImpl(MethodImplOptions.InternalCall)]
internal static extern int GetHashCode(IHashCodeGenerator hashGenerator);
[MethodImpl(MethodImplOptions.InternalCall)]
internal static extern Type GetType(ITypeIdentifiable typedInstance);
[MethodImpl(MethodImplOptions.InternalCall)]
internal static extern IMemberwiseCloneable MemberwiseClone(IMemberwiseCloneable original);
}
// let's say that as a rule the compiler implicitly makes all classes implement these interfaces
class MyClassExampleA : IEquatable, IHashCodeGenerator, ITypeIdentifiable, IConvertibleToString, IMemberwiseCloneable
{
// The compiler also implicitly makes all classes implement the interfaces with the following code (unless otherwise specified)
#region IEquatable Members
public bool Equals(IEquatable other)
{
// let's suppose that this is equivalent to the current implementation of Object.Equals
return ClrInternals.Equals(this, other);
}
#endregion
#region IHashCodeGenerator Members
public int GetHashCode()
{
// let's suppose that this is equivalent to the current implementation of Object.GetHashCode
return ClrInternals.GetHashCode(this);
}
#endregion
#region ITypeIdentifiable Members
public Type GetType()
{
// let's suppose that this is equivalent to the current implementation of Object.GetType
return ClrInternals.GetType(this);
}
#endregion
#region IConvertibleToString Members
public string ToString()
{
// let's suppose that this is equivalent to the current implementation of Object.ToString
return this.GetType().ToString();
}
#endregion
// this one is perhaps a little goofy, since it doesn't satisfy any interface
// In order to be equivalent to the current Object.MemberwiseClone implementation, I've made this protected,
// but we cannot have a protected method that implements an interface, so this throws a wrench into things.
protected MyClassExampleA MemberwiseClone()
{
// let's suppose that this is equivalent ot the current implementation of Object.MemberwiseClone
return (MyClassExampleA)ClrInternals.MemberwiseClone(this);
}
// ** All of the above code is just a representation of the implicit semantics that the compiler/CLR applies to a class. Perhaps this code is not actually generated by the compiler for each class (that would be a lot of duplication!), but rather the CLR might handle this logic internally
}
// Ok, so now I'm implementing a general Stack class
public class Stack
{
// what type should I use for the parameter?
// I have five different interfaces to choose from that I know all classes implement, but which one should I pick?
public void Push(type??? item)
{
// ...
}
// what type should I use for the return type?
// I have five interfaces to choose from, but if I return one,
// then my caller can't utilize the methods defined in the other interfaces without casting.
// I know all classes implement all five interfaces, but is it possible that my Stack might also contain non-class objects that don't implement all interfaces? In that case it might be dangerous for the caller to cast the return value from one interface to another.
public type??? Pop()
{
// ...
}
// In C++ I could have used void* or defined the Stack class as a template
}
// moving on...
class StackUtilizer
{
// here I try to utilize the Stack class
public void UseStack(Stack stack)
{
// what type should I use for the variable to hold the result of the Stack.Pop method?
type??? item = stack.Pop();
// if I use IEquatable
IEquatable item1 = stack.Pop();
IEquatable item2 = stack.Pop();
item1.Equals(item2); // then I can do this
Type itemType = item1.GetType(); // but I can't do this
string s = item1.ToString(); // nor can I do this
// Ok, this calls for another interface that composes all of these other interfaces into one
}
}
// let's define a single interface that pulls all of these other interfaces together
public interface IObject : IEquatable, IHashCodeGenerator, ITypeIdentifiable, IConvertibleToString, IMemberwiseCloneable
{
// no need to define any methods on this interface. The purpose of this interface is merely to consolidate all of these other basic interfaces together.
}
// now we change the compiler rule to say that all classes implicitly implement the IObject interface
class MyClassExampleB : IObject
{
// ... <refer to MyClassExampleA for the implicit implementation of the interfaces>
}
// now let's try implementing that Stack class again
public class Stack
{
// I know that all classes implement the IObject interface, so it is an acceptable type to use as a parameter
public void Push(IObject item)
{
// ...
}
// again, since all classes implement IObject, I can use it as the return type
public IObject Pop()
{
// ...
throw new NotImplementedException("This is an example. The implementation of this method is irrelevant.");
}
}
class StackUtilizer
{
// here I try to utilize the Stack class
public void UseStack(Stack stack)
{
// now I can just use IObject for my variables holding the return value of the Stack.Pop method
IObject item = stack.Pop();
// if I use IObject
IObject item1 = stack.Pop();
IObject item2 = stack.Pop();
item1.Equals(item2); // then I can do this
Type itemType = item1.GetType(); // and I can do this
string s = item1.ToString(); // and I can do this
}
}
所以，最后我们还是有一个 IObject 接口，类似于现在的 System.Object 类。悬而未决的问题是编译器/CLR 将如何处理强制执行我们的规则，即所有类都实现 IObject 接口。
我可以想到三种可能的方法：
- 编译器为每个类生成隐式接口实现，会造成大量重复。
- CLR 将以一种特殊的方式处理这些接口实现，不需要编译器为每个类实际生成代码。
- 我们定义了一个基类，我们称它为
Object（听起来很熟悉？），它实现了IObject 接口，我们将规则更改为所有类都隐式继承自Object（这正是我们今天所拥有的，但没有接口）。