紧急求助：out子类不能转化为out基类？

[chelsea]

public class Base{
}
public class Sub:Base{
}

public class Test{
Sub sub;
void test(){
func(out sub);
}

void func(out Base obj){
obj = new Sub();
}
}
C:\......\element.cs(29):
参数“1” : 无法从“out ClassLibrary1.NewFolder1.xpdl.Sub”转换为
“out ClassLibrary1.NewFolder1.xpdl.Base”

[chelsea]

我现在认为是如果允许转换的化，将无法保证类型安全性:

func(out Base b){
b = new OtherSubClass();
}

Sub sub;
OtherSubClass osub;
func(out sub); //error
func(out osub);//ok

违反那个什么Liskov替换原则

[qiume]

由于在函数间传递对象的时候，本身就是引用传递，
所以应改为:
public class Base
{
}
public class Sub:Base
{
}

public class Test
{
Sub sub;
void test()
{
func(sub);
}

void func(Base obj)
{
obj = new Sub();
}
}

[qiume]

或者:
public class Base
{
}
public class Sub:Base
{
}

public class Test
{
void test(Sub sub)
{
func(sub);
}

void func(Base obj)
{
obj = new Sub();
}
}

[chelsea]

有点天真，不过还是谢谢