Why does C# not allow const and static on the same line?

Question

Why does C# not allow const and static on the same line? In Java, you must declare a field as \'static\' and \'final\' to act as a constant. Why does C# not let you declare co

Answer 1

const and static really do mean different things, different storage mechanism, different initialisation. static is read/write, therefore must have memory allocated for storage and must be initialised at runtime. A static can be initialised with a literal value or an expression. In contrast, a const is immutable and must be initialised with a compile time constant (typically a literal value, or an expression that can be fully evaluated at compile time). The value is known at compile time so it can be embedded directly in the generated code, therefore requires no storage to be allocated at runtime.

Answer 2

As said before, static final in Java is the same as static readonly in C#. In fact, you are saying that this member is static and its content can't be changed. Also you can specify in both cases the value from static constructor.

But const in C# is completely different thing. It's more along the lines of constants in C (DEFINE directives) but with OOP in mind. It's static because it's constant - every instance would have this constant with the same value, no constructor can set it. Also it's possible that someone would like to access the constant without having to create an instance. When you think about it non-static constant just doesn't make sense. You can almost say that constants are not part of an object - they just use it to provide context, a strong name.

Java doesn't have an equivalent to const. You can read somewhere that static final is equivalent to DEFINE but that's just so vague. Completely different mechanism, nothing in common but in the end result in the code is the same - better maintainability and readability of the code.

You just have to stop thinking about constants in C# as static members because they are not. Think of them as OOP version of DEFINE. When you consider encapsulation only reason for final and readonly fields is to prevent your own code from accidently changing its value. And that doesn't sound like constant to me.

Sumary:

• final = readonly
• static final = static readonly
• N/A = const

Answer 3

Constants by their nature are static, so that would be redundant.

Answer 4

It is true that a C# const implies static BUT, C# has an equivalent to Java's final keyword in the keyword readonly.

So, in fact, C# allows a const final, it is static readonly in C#.

Answer 5

Because allowing and not requiring modifiers that are inherent can cause confusion. If you see

static const int A = 3
const int B = 5

you may believe that they are 2 different kinds of constants.
Even VB 2008 (which can be very verbose if you wish) doesn't allow that.