c# - const, readonly 和 get 在静态类中有什么区别

Question

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Answer 1

声明为只读的成员提供了在类的(静态)构造函数中更改的可能性，而 const 成员不能在运行时更改。

将字段声明为 const 使其自动静态，引用 §10.3.7:

When a field, method, property, event, operator, or constructor declaration includes a static modifier, it declares a static member. In addition, a constant or type declaration implicitly declares a static member.

第三个只是一个只读属性，恰好总是返回 5。

您永远不应该使用这样的属性，并尽可能使用 const 成员，以允许编译器和/或抖动执行它们的优化并帮助其他人阅读您的代码(该属性对我来说是一种 WTF) .如果需要在程序启动期间初始化的常量值(例如，机器的核心数)，则必须使用静态只读成员。

这是 C# 规范 (§10.5.2.1) 中的一个很好的例子:

A static readonly field is useful when a symbolic name for a constant value is desired, but when the type of the value is not permitted in a const declaration, or when the value cannot be computed at compile-time. In the example

public class Color
{
    public static readonly Color Black = new Color(0, 0, 0);
    public static readonly Color White = new Color(255, 255, 255);
    public static readonly Color Red = new Color(255, 0, 0);
    public static readonly Color Green = new Color(0, 255, 0);
    public static readonly Color Blue = new Color(0, 0, 255);
    private byte red, green, blue;
    public Color(byte r, byte g, byte b) {
        red = r;
        green = g;
        blue = b;
    }
}

the Black, White, Red, Green, and Blue members cannot be declared as const members because their values cannot be computed at compile-time. However, declaring them static readonly instead has much the same effect.

还有另一个区别(§10.5.2.2):

Constants and readonly fields have different binary versioning semantics. When an expression references a constant, the value of the constant is obtained at compile-time, but when an expression references a readonly field, the value of the field is not obtained until run-time.

因此，总而言之，即使乍一看它们可能看起来很相似，它们也有很大的不同，您应该使用最适合您意图的那个。