问题描述
属性预期性能类似的字段，即使它们真的功能。什么可以说对任意业绩预期的IEnumerable ？
Properties are expected to perform similarly to fields, even though they are really functions. What can be said about the expected performance of an arbitrary IEnumerable?
它是公平的，从性能借用的概念，并说，一个的IEnumerable 应该执行大致相同迭代数组或名单，其中，T＆GT; ？
Is it fair to borrow the concept from properties and say that an IEnumerable should perform about the same as iterating an array or List<T>?
或者是它没关系几乎任何发生在每次迭代：数据库访问，Web服务调用，耗时的计算等。
Or, is it okay for just about anything happen with each iteration: database access, web service call, time-consuming computation, etc.
推荐答案
在谈到从经验，你真的不能推断出任何关于任意的IEnumerable 的性能。例如，它可能是一个的IQueryable 的化身，每次枚举时命中数据库。或者，它可能的结果 File.EnumerateLines 。
Speaking from experience you can't really infer anything about the performance of an arbitrary IEnumerable. For example, it might be an IQueryable in disguise, hitting the database every time it is enumerated. Or it might be the result of File.EnumerateLines.
有时候，重要的是可枚举只能用一次列举
Sometimes it is important that the enumerable only be enumerated once.
这是相对于一个属性。如果一个属性是访问数据库或读我档案我会认为这是一个code气味。对于的IEnumerable 这只是正常的。
This is in contrast to a property. If a property was to hit the database or read I file I'd consider this to be a code smell. For an IEnumerable it is just normal.
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