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。
使用var而不是显式类型使重构更容易(因此我必须反驳前面的帖子，他们的意思是它没有区别，或者它纯粹是“语法糖”)。
您可以更改方法的返回类型，而无需更改调用此方法的每个文件。想象一下
...
List<MyClass> SomeMethod() { ... }
...
就像这样
...
IList<MyClass> list = obj.SomeMethod();
foreach (MyClass c in list)
System.Console.WriteLine(c.ToString());
...
如果您希望重构SomeMethod()以返回IEnumerable<MySecondClass>，则必须在使用该方法的每个地方更改变量声明(也在foreach中)。
如果你写
...
var list = obj.SomeMethod();
foreach (var element in list)
System.Console.WriteLine(element.ToString());
...
相反，你不需要改变它。
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.
