Question

I was plugging away on an open source project this past weekend when I ran into a bit of code that confused me to look up the usage in the C# specification.

The code in questions is as follows:

internal static class SomeStaticClass
{
    private const int CommonlyUsedValue = 42;

    internal static string UseCommonlyUsedValue(...)
    {
        // some code
        value = CommonlyUsedValue + ...;

        return value.ToString();
    }
}

I was caught off guard because this appears to be a non static field being used by a static function which some how compiled just fine in a static class!

The specification states (§10.4):

A constant-declaration may include a
set of attributes (§17), a new
modifier (§10.3.4), and a valid
combination of the four access
modifiers (§10.3.5). The attributes
and modifiers apply to all of the
members declared by the
constant-declaration. Even though
constants are considered static
members, a constant-declaration
neither requires nor allows a static
modifier. It is an error for the same
modifier to appear multiple times in a
constant declaration.

So now it makes a little more sense because constants are considered static members, but the rest of the sentence is a bit surprising to me. Why is it that a constant-declaration neither requires nor allows a static modifier? Admittedly I did not know the spec well enough for this to immediately make sense in the first place, but why was the decision made to not force constants to use the static modifier if they are considered static?

Looking at the last sentence in that paragraph, I cannot figure out if it is regarding the previous statement directly and there is some implicit static modifier on constants to begin with, or if it stands on its own as another rule for constants. Can anyone help me clear this up?

Answer 1

Basically, const implies static already, since the value cannot be changed at runtime. There’s no reason for you to ever declare static const, since it’s already implied, and the language designers decided to make the language syntax reflect that.

The specification language is basically saying “Const is always static, so you can’t explicitly say static and const since it’s redundant.”