.NET 泛型 : Is it possible to enforce abstract class on generic type

Question

我有以下代码:

void DoSomething<T>() where T : class
{
    if(typeof(T).IsAbstract)
         // do something with T
    else
         // throw an error
}

是否可以强制 T 是泛型定义中的抽象类(类似于 where T : abstract class)？

Answer 1

这是不可能的。参见 C# 规范的第 10.1.5 节。特别是，语法非常清楚地表明这是不可能的。

type-parameter-constraints-clauses:
    type-parameter-constraints-clause
    type-parameter-constraints-clauses   type-parameter-constraints-clause
type-parameter-constraints-clause:
    where   type-parameter   :   type-parameter-constraints
type-parameter-constraints:
    primary-constraint
    secondary-constraints
    constructor-constraint
    primary-constraint   ,   secondary-constraints
    primary-constraint   ,   constructor-constraint
    secondary-constraints   ,   constructor-constraint
    primary-constraint   ,   secondary-constraints   ,   constructor-constraint
primary-constraint:
    class-type
    class
    struct
secondary-constraints:
    interface-type
    type-parameter
    secondary-constraints   ,   interface-type
    secondary-constraints   ,   type-parameter
constructor-constraint
    new   (   )

您可以在方法主体中包含一个保护子句:

Contract.Requires<InvalidOperationException>(!typeof(T).IsAbstract);