为什么我们在C＃中将内部类用于常量？

Question

I have seen it in many projects. Why do developers use internal classes to store the constant variables in C#?

For instance:

internal static class Constants
{
    public const double Pi = 3.14159;
    public const int SpeedOfLight = 300000; // km per sec.
}

Answer 1

Simply, the designer decided that this class need to be used within the same assembly. And it is not to be exposed to or accessed from any project referencing the assembly.

When you download a Nuget package, you can't access classes that are internal. The developers decided that you don't need to access these. So these values are "private" for this package.

More on access modifiers:

public :Access is not restricted.

protected :Access is limited to the containing class or types derived from the containing class.

internal: Access is limited to the current assembly.

protected internal : Access is limited to the current assembly or types derived from the containing class.

private : Access is limited to the containing type.

Answer 2

While most answers describe the meaning of internal they are missing a part of the question I think: Why put constants in a inner class?

This is mostly because it can they desire to identify constants through something feeling like a namespace:

double myValue = Constants.Pi * 10;

Or

double myValue = OtherClass.Constants.Pi * 10;

Without the inner class they would look more like members/properties. At least when they do not use UPPER_CASING for the naming.

To make the answer complete: The internal is used to protect the constant against using them outside of the assembly.