MSDN给出了答案: 在类和结构之间选择。

基本上，这个页面给你一个4项清单，并告诉你使用一个类，除非你的类型满足所有的标准。

不定义结构，除非 类型包含以下所有内容 特点: 它在逻辑上表示一个值，类似于基本类型 (整数，双精度，等等)。 实例大小小于16字节。 它是不可变的。 它不需要经常装箱。

当您需要值类型语义而不是引用类型时，请使用结构。结构体是按值复制的，所以要小心!

另见以前的问题，例如:

.NET中struct和class的区别是什么?

当您不需要行为，但需要比简单的数组或字典更多的结构时。

跟进 这就是我对结构体的一般看法。我知道他们可以有方法，但我喜欢保持整体的精神区分。

正如@Simon所说，结构体提供了“值类型”语义，所以如果你需要类似于内置数据类型的行为，可以使用结构体。由于结构体是通过复制传递的，所以要确保它们的大小很小，大约16字节。

If an entity is going to be immutable, the question of whether to use a struct or a class will generally be one of performance rather than semantics. On a 32/64-bit system, class references require 4/8 bytes to store, regardless of the amount of information in the class; copying a class reference will require copying 4/8 bytes. On the other hand, every distinct class instance will have 8/16 bytes of overhead in addition to the information it holds and the memory cost of the references to it. Suppose one wants an array of 500 entities, each holding four 32-bit integers. If the entity is a structure type, the array will require 8,000 bytes regardless of whether all 500 entities are all identical, all different, or somewhere between. If the entity is a class type, the array of 500 references will take 4,000 bytes. If those references all point to different objects, the objects would require an additional 24 bytes each (12,000 bytes for all 500), a total of 16,000 bytes--twice the storage cost of a struct type. On the other hand, of the code created one object instance and then copied a reference to all 500 array slots, the total cost would be 24 bytes for that instance and 4,000 for the array--a total of 4,024 bytes. A major savings. Few situations would work out as well as the last one, but in some cases it may be possible to copy some references to enough array slots to make such sharing worthwhile.

如果实体应该是可变的，那么使用类还是结构的问题在某些方面会更容易。假设“Thing”是一个具有整数字段x的结构体或类，并执行以下代码:

  Thing t1,t2;
  ...
  t2 = t1;
  t2.x = 5;

是否希望后一种说法影响t1.x?

如果Thing是类类型，t1和t2将等效，即t1。X和t2。X也是等价的。因此，第二个语句将影响t1.x。如果Thing是一个结构类型，t1和t2将是不同的实例，即t1。X和t2。X表示不同的整数。因此，第二个语句不会影响t1.x。

Mutable structures and mutable classes have fundamentally different behaviors, though .net has some quirks in its handling of struct mutations. If one wants value-type behavior (meaning that "t2=t1" will copy the data from t1 to t2 while leaving t1 and t2 as distinct instances), and if one can live with the quirks in .net's handling of value types, use a structure. If one wants value-type semantics but .net's quirks would cause lead to broken value-type semantics in one's application, use a class and mumble.

除了以上精彩的回答:

结构是值类型。

它们永远不能被设置为“无”。

设置一个结构= Nothing，将其所有的值类型设置为默认值。