C＃是where（）和where （）之间的区别

In C# linq, is there a difference between A.where(...) and A.where<SomeClass>(...) where A is some type of suitable collection?

在C#linq中,A.where(...)和A.where (...)之间有区别吗?其中A是某种合适的集合类型?

1 个解决方案

#1

In general no, because the compiler will infer the type T of the IEnumerable<> A and use as the generic parameter of the .Where<>()

通常不会,因为编译器会推断IEnumerable <> A的类型T并用作.Where <>()的泛型参数

but

You could force the Where<> to "use" a SomeClass that is a base class of the T type of the IEnumerable<> (this works because IEnumerable<> is covariant, so IEnumerable<subclass> can be "casted" to IEnumerable<baseclass>)...

你可以强制Where <>“使用”一个SomeClass,它是IEnumerable <>的T类型的基类(这是因为IEnumerable <>是协变的,所以IEnumerable 可以“转换”为IEnumerable <基类> )...

The only practical result would be that you would "see" in the Where() a little "less" of T (and that if there are properties/methods of T that are "overwritten" by SomeClass you will access them without having to do casts)

唯一可行的结果是你会在Where()中“看到”一点“少”的T(并且如果T的属性/方法被SomeClass“覆盖”,你将无需访问它们铸)

Example:

public class MyClass
{
    public int GetNumber()
    {
        return 1;
    }
}

public class MySubClass : MyClass
{
    // Note the use of *new*. This isn't a virtual method!
    public new int GetNumber()
    {
        return 2;
    }
}

MySubClass[] coll = new[] { new MySubClass(), new MySubClass() };
var res = coll.Where(x => x.GetNumber() == 2).ToArray(); // 2 elements
var res2 = coll.Where<MyClass>(x => x.GetNumber() == 2).ToArray(); // 0 elements
var res3 = coll.Where<MyClass>(x => x.GetNumber() == 1).ToArray(); // 2 elements

#1