什么是C＃的lambda变量的范围有多大？ [英] What is the scope of a lambda variable in C#?

问题描述

我困惑的拉姆达变量的范围，就拿以下

I'm confused about the scope of the lambda variable, take for instance the following

var query = 
    from customer in clist
    from order in olist
    .Where(o => o.CustomerID == customer.CustomerID && o.OrderDate ==  // line 1
        olist.Where(o1 => o1.CustomerID == customer.CustomerID)        // line 2
             .Max(o1 => o1.OrderDate)                                  // line 3
    )
    select new {
        customer.CustomerID,
        customer.Name,
        customer.Address,
        order.Product,
        order.OrderDate
    };

在1号线我有声明的lambda变量的'o'，这意味着我不能在网上再次声明2（或至少编译器会抱怨，如果我尝试）
但这并不抱怨3号线，即使'01'已经存在??

In line 1 I have declare a lambda variable 'o' which means I cannot declare it again in line 2 (or at least the compiler complains if I try to) But it doesn't complain about line 3 even though 'o1' already exists??

？一个lambda变量的范围是什么

What is the scope of a lambda variable?

推荐答案

括号给出线索 - 拉姆达变量在哪里范围抓获它宣称：

The brackets give the clue - the lambda variable is captured in the scope of where it's declared:

.Where(o => ... olist.Where(o1 => ...).Max(o1 => ...))
  //  |----------------------------------------------| scope of o
  //                       |---------|                 scope of first o1
  //                                      |---------|  scope of second o1

注意有两个 01 变量，但他们都重叠（或阴影）的 0 变量，因此不能使用相同的名称。

Note that there's no overlap for the two o1 variables, but they both overlap (or shadow) the o variable and hence can't use the same name.

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