如果我有一个lambda,如()=> {throw new Exception(); },不清楚它是否具有返回类型.因此,它可以(隐式地)转换为Action和Func< object> (或任何其他Func T).这是因为,根据§6.5C#4规范的匿名函数转换：
[A] delegate type
Dis compatible with an anonymous functionFprovided:
…
If
Dhas avoidreturn type and the body ofFis a statement block,when […] the body ofFis a valid statement block in which no return statement specifies an expression.If
Dhas a non-void return type and the body ofFis a statement block,when […] the body ofFis a valid statement block with a non-reachable end point in which eachreturnstatement specifies an expression that is implicitly convertible to the return type ofD.
但是如果我有一个方法的两个重载,其中一个具有Action类型的参数和另一个Func< object>,并且我从上面传递了lambda,那么Func< object>使用过载.为什么？规范的哪一部分说Func< object>在这种情况下比行动好吗？
我看过§7.5.3.2更好的功能成员,但这并没有解释.
解决方法
Given an implicit conversion
C1that converts from an expressionEto a typeT1,and an implicit conversionC2that converts from an expressionEto a typeT2,C1is a better conversion thanC2if at least one of the following holds:
…
Eis an anonymous function,T1is either a delegate typeD1or an expression tree typeExpression<D1>,T2is either a delegate typeD2or an expression tree typeExpression<D2>and one of the following holds:
…
D1andD2have identical parameter lists,and one of the following holds:
…
D1has a return typeY,andD2is void returning
