在与同事讨论了c# 3中var关键字的使用后，我想知道人们对通过var适当使用类型推断的看法是什么?
例如，我很懒地在有问题的情况下使用var，例如:-
foreach(var item in someList) { // ... } // Type of 'item' not clear.
var something = someObject.SomeProperty; // Type of 'something' not clear.
var something = someMethod(); // Type of 'something' not clear.
var更合法的用法如下:-
var l = new List<string>(); // Obvious what l will be.
var s = new SomeClass(); // Obvious what s will be.
有趣的是，LINQ似乎是一个灰色区域，例如:-
var results = from r in dataContext.SomeTable
select r; // Not *entirely clear* what results will be here.
结果很明显，因为它将是一个实现IEnumerable的类型，但它并不完全明显，与var声明一个新对象的方式相同。
当涉及到对象的LINQ时，情况就更糟了，例如:-
var results = from item in someList
where item != 3
select item;
这并不比等价的foreach(var item in someList){//…}相当于。
这里有一个关于类型安全的真正问题——例如，如果我们将该查询的结果放在一个接受IEnumerable<int>和IEnumerable<double>的重载方法中，调用者可能会无意中传入错误的类型。
Var确实保持强类型，但问题是，在定义中不立即显示类型是否危险，当重载意味着当你无意中将错误的类型传递给方法时，编译器可能不会发出错误，这种情况会被放大。
Var，在我看来，在c#中是一个很好的东西。任何这样类型的变量仍然是强类型的，但是它从赋值函数的右边得到它的类型。因为类型信息在右侧可用，在大多数情况下，也必须在左侧输入它是不必要的和过于冗长的。我认为这在不降低类型安全性的情况下显著提高了可读性。
From my perspective, using good naming conventions for variables and methods is more important from a readability perspective than explicit type information. If I need the type information, I can always hover over the variable (in VS) and get it. Generally, though, explicit type information shouldn't be necessary to the reader. For the developer, in VS you still get Intellisense, regardless of how the variable is declared. Having said all of that, there may still be cases where it does make sense to explicitly declare the type -- perhaps you have a method that returns a List<T>, but you want to treat it as an IEnumerable<T> in your method. To ensure that you are using the interface, declaring the variable of the interface type can make this explicit. Or, perhaps, you want to declare a variable without an initial value -- because it immediately gets a value based on some condition. In that case you need the type. If the type information is useful or necessary, go ahead and use it. I feel, though, that typically it isn't necessary and the code is easier to read without it in most cases.
您可以让编译器(以及接下来维护代码的人员)从初始化式赋值的右边推断类型。如果这种推断是可能的，编译器可以这样做，从而节省了您的一些输入。
如果这个推断对那个可怜的家伙来说很容易，那么你没有伤害到任何东西。如果推断很难，那么作为一般规则，您已经使代码更难维护
我不会这么做的。
Lastly, if you intended the type to be something particular, and your initializer expression actually has a different type, using var means it will be harder for you to find the induced bug. By explicitly telling the compiler what you intend the type to be, when the type isn't that, you would get an immediate diagnostic. By sluffing on the type declaration and using "var", you won't get an error on the initialization; instead, you'll get a type error in some expression that uses the identifier assigned by the var expression, and it will be harder to understand why.
寓意是，要谨慎使用var;您通常不会给您自己或您的下游维护人员带来很多好处。并希望他的理由是一样的，这样你就不会因为他认为使用var很容易而猜测他的意图。在编写一个具有较长生命周期的系统时，优化输入量是一个错误。
