今天看到了一句话
the Where() LINQ extension method is used to filter for a particular set of URLs. Where(), like most LINQ methods, returns an IEnumerable value
让我好奇IEnumerable Icollection Ilist list之间到底是什么关系
顺带IEnumerable可以直接调用ToList变成list

1 All LINQ queries must start with the ‘var’ keyword. In fact, the very purpose of the ‘var’ keyword is to start a LINQ query!

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string[] people = new [] { "Tom", "Dick", "Harry" };
var filteredPeople = people.Where (p => p.Length > 3); 
//is precisely equivalent to:

string[] people = new [] { "Tom", "Dick", "Harry" };
IEnumerable<string> filteredPeople = people.Where (p => p.Length > 3);