[英]C# delegate argument type
delegate void Dele(string str);
delegate void Alli(int num);
class Program
{
static void Main(string[] args)
{
Dele dele = Test; // O
Alli alli = Test; // X
}
static void Test(object obj) { }
}
Alli alli = Test; // X
Why???为什么???
Maybe...也许...
str as object
( O ) str as object
( O )
num as object
( X ) num as object
( X )
??? ???
(Sorry, I'm not good at English) (对不起,我英语不好)
(It looks like your post is mostly code; please add some more details.: OK) (看起来你的帖子主要是代码;请添加更多细节。:好的)
This behaviour is specified in the C# language specification.此行为在 C# 语言规范中指定。
Here:这里:
Dele dele = Test;
You are doing a method group conversion .您正在进行方法组转换。 One of the requirements for a method group conversion to be allowed is that
允许方法组转换的要求之一是
The selected method M must be compatible (Delegate compatibility) with the delegate type D, or otherwise, a compile-time error occurs.
选择的方法 M 必须与委托类型 D 兼容(委托兼容性),否则会发生编译时错误。
Delegate compatibility is specified like this (emphasis mine): 委托兼容性是这样指定的(强调我的):
A method or delegate M is compatible with a delegate type D if all of the following are true:
如果满足以下所有条件,则方法或委托 M 与委托类型 D 兼容:
- D and M have the same number of parameters, and each parameter in D has the same ref or out modifiers as the corresponding parameter in M.
D 和 M 具有相同数量的参数,并且 D 中的每个参数与 M 中的相应参数具有相同的 ref 或 out 修饰符。
- For each value parameter (a parameter with no ref or out modifier), an identity conversion (Identity conversion) or implicit reference conversion (Implicit reference conversions) exists from the parameter type in D to the corresponding parameter type in M.
对于每一个值参数(没有 ref 或 out 修饰符的参数),从 D 中的参数类型到 M 中对应的参数类型都存在一个身份转换(Identity conversion)或隐式引用转换(Implicit reference conversions)。
- For each ref or out parameter, the parameter type in D is the same as the parameter type in M.
对于每个 ref 或 out 参数,D 中的参数类型与 M 中的参数类型相同。
- An identity or implicit reference conversion exists from the return type of M to the return type of D.
从 M 的返回类型到 D 的返回类型存在标识或隐式引用转换。
There is an implicit reference conversion from string
to object
, because string
is a subclass of object
, but there isn't an implicit reference conversion from int
to object
.存在从
string
到object
的隐式引用转换,因为string
是object
的子类,但没有从int
到object
的隐式引用转换。 int
is a value type, so the conversion is actually a boxing conversion . int
是一个值类型,所以转换实际上是一个装箱转换。 Therefore, the method group conversion does not work for Alli
and Test
.因此,方法组转换不适用于
Alli
和Test
。
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