Can I force a dependency between namespaces in C#

Question

Can I restrict classes from a specific namespace from referencing classes in another specific namespace? Both namespaces exist in the same .NET assembly.

Example:

namespace LegacyCode
{
    class LegacyClass { ... }
}

namespace NewCode
{
    class NewClass {...}
}

I do not want classes from 'NewCode' to be able to reference classes in 'LegacyCode'.

Options:

1. Have different assemblies (makes deployment harder, build takes longer)
2. Using a tool like NDetect (costs money!)

Does anyone have any other ideas?

Answer 1

Document the design, talk to people, review code. Don't try to throw technology at people problems. (The review part can become more effective with tools like NDetect, though.)

If you really need the isolation of design changes, go for separate assemblies: that's the intended design mechanism. But be sure you have a reasonable versioning scheme both for the interface and the implementation.

Answer 2

I think separate assemblies are the only possible solution.

Answer 3

MS uses the System.ObsoleteAttribute attribute to mark obsolete/legacy code. This attribute provides an ctor that creates a compiler error. Though, I'd use this if there are not too many legacy classes.

Answer 4

Consider marking the classes with the Obsolete attribute. This will cause any code that isn't itself marked as 'Obsolete' to generate a warning during compilation.

Enable 'Treat warnings as errors' setting on the 'Build' tab of the project file to cause this warning to fail compilation with an error instead.

Edit:

Agree that seperate assemblies is a good strategy to facilitate fading out this code. This won't stop people referring to it though. The obsolete attribute makes it clear that this code is, um, obsolete.

Edit #2:

Thanks to Dan Tao for pointing out the overloaded constructor of the Obsolete attribute. This means you can enforce whether usage of a something should be treated as an error or not, without having to enable treat warnings as errors. There is also usefully the option to specify a message instructing the user of a workaround. This message is displayed during compilation in the error/warning.

Answer 5

As others have said, use the obsolete attribute (Even if you have to rename it).

But go one step further. DELETE ANY Legacy method that is NO longer used as soon as possible. This will prevent someone from using it later. You should start to see the Compiler warnings due to the obsolete attributes to drop over time.

You might even make it a daily one hour long test to eliminate as many compiler warnings as you can... Maybe you pitch in to buy the daily winner a beer (or soft drink..;) after work.