强制C＃方法只传递正参数？

Question

I want to force my method to only accept an integer parameter if it is positive . If the method is passed a negative integer it should throw a compile time error. What is the best way to achieve this?

Currently I am using Math.Abs(Int) inside the method, but I want the error to be at compile time.

Answer 1

Just make the parameter a uint or a ushort . That will prevent negative input at compile-time. It won't prevent 0, however... I assume you're really after non-negative input rather than strictly positive input.

If your method has to accept a signed parameter, then:

• You can validate the argument value, throwing an exception if it's invalid. (This is a much better idea than using Math.Abs to try to "fix" invalid input.)
• You could use Code Contracts to indicate to other code that the parameter should have a non-negative value, and it will attempt to prove that everywhere you call the method, the value will be non-negative. This won't be enforced by the C# compiler, but it can still be a build-time procedure.

If you go with the exception approach, then you should also have a comprehensive set of unit tests around the code calling your method - and that code should validate its inputs as well, of course.

Answer 2

You can use Code Contracts (and link ) and do a static code analysis before compiling, then using:

Contract.Requires( parameter >= 0 );

Static code analysis is limited, and you should NOT limit to code contracts (you should still throw runtime exceptions). It'll catch obvious things (like passing constants), but will not catch passing in negative values when they come from outside your code (read from disk, from a database, or whatever).

That's just not possible at compile time