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。
我认为var的使用应该与明智选择的变量名称相结合。
我在foreach语句中使用var没有问题，前提是它不是这样的:
foreach (var c in list) { ... }
如果是这样的话:
foreach (var customer in list) { ... }
．.． 这样，阅读代码的人就更有可能理解什么是“列表”。如果您可以控制列表变量本身的名称，那就更好了。
这同样适用于其他情况。这是非常无用的:
var x = SaveFoo(foo);
．.． 但这是有道理的:
var saveSucceeded = SaveFoo(foo);
各有各的，我想。我发现自己这样做，简直是疯了:
var f = (float)3;
我需要一个12步的var程序。我叫Matt，我(ab)使用var。
将它用于匿名类型—这就是它存在的目的。其他的都是徒劳无功。像许多使用C长大的人一样，我习惯于查看类型声明的左侧。除非迫不得已，我是不会看右边的。在任何旧的声明中使用var都让我一直这样做，我个人觉得不舒服。
Those saying 'it doesn't matter, use what you're happy with' are not seeing the whole picture. Everyone will pick up other people's code at one point or another and have to deal with whatever decisions they made at the time they wrote it. It's bad enough having to deal with radically different naming conventions, or - the classic gripe - bracing styles, without adding the whole 'var or not' thing into the mix. The worst case will be where one programmer didn't use var and then along comes a maintainer who loves it, and extends the code using it. So now you have an unholy mess.
标准是一件好事，因为它们意味着你更有可能捡起随机代码，并能够快速地理解它。不同的东西越多，就越难。而转移到“无处不在的var”风格会有很大的不同。
I don't mind dynamic typing, and I don't mind implict typing - in languages that are designed for them. I quite like Python. But C# was designed as a statically explicitly-typed language and that's how it should stay. Breaking the rules for anonymous types was bad enough; letting people take that still further and break the idioms of the language even more is something I'm not happy with. Now that the genie is out of the bottle, it'll never go back in. C# will become balkanised into camps. Not good.
