问题描述
参照，据我了解，下面是不是在C＃支持：
VAR FUNC =（X，Y）=>将Math.log（X）+将Math.log（Y）;
不过，我可以创建一个方法，函数功能的格式为：
公共静态Func键< T，T，T> FUNC< T>（FUNC< T，T，T&F）的温度= GT; F;
然后执行：
VAR func =函数<双>（（X，Y）=>将Math.log（X）+将Math.log（Y））;
这将编译就好了。然而，对于不同类型的参数和返回值的lambda表达式，事情就变得奇怪。举例来说，如果我有一个方法：
公共静态Func键< T1，T2，T3> FUNC&所述的T1，T2，T3>（FUNC&下; T1，T2，T3和F）的温度= GT; F;
我可以为例子做的：
VAR func =函数（（双X，双Y）=> ${X + Y}）;
和太会编。因此，C＃编译器似乎能够推断出返回类型的lambda。但是，以下不会编译：
VAR func =函数（（X，Y）=>将Math.log（ X）+将Math.log（Y））;
编译器似乎是不能够推断出类型第X 和是从它们在体内使用的方式。
所以，我的问题：什么是对lambda表达式类型推断的明确规则;会出现什么编译器推断出，哪些不是吗？
The definitive rules are in the specification. If you want to look at the implementation, you can find it easily enough in the Roslyn sources; I commented it pretty heavily, anticipating that there would be questions. Note that in particular the comment starting around line 110 is relevant to your question; study this carefully if you want a deep understanding of how lambda type inference works.
Consider compiling the compiler yourself in debug mode; you can then use the Dump method at breakpoints to describe the state of the type inference engine as it goes. I used this to facilitate more rapid debugging, and when considering extensions to the algorithm. (Some of which are still in the code, commented out.)
That is far too broad a question to answer definitively. But the basic action with respect to the examples in your question is:
- Bounds on type parameters are inferred from ordinary arguments matched with formal parameter types.
- Lambdas where all formal parameter types of the lambda are inferred or known have their return types inferred
- The previous step is repeated until the algorithm fails to make progress or deduces a contradiction.
I recorded a video -- ten years ago now -- explaining all this step by step but apparently it is no longer on MSDN. I am vexed.
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