README.md

Durian.InterfaceTargets, similar to how the System.AttributeUsageAttribute works, allows to specify member kinds an interface can be implemented by.

1. Structure
2. Setup
3. Basics
4. Reflection
5. Possible values

Structure

Packages that are part of the InterfaceTargets module:

• Durian.InterfaceTargets

InterfaceTargets provides 2 types:

• Durian.InterfaceTargets
• Durian.InterfaceTargetsAttribute

Setup

To start using InterfaceTargets, reference either the Durian.InterfaceTargets or Durian package.

Note: Like with other Durian modules, the target project must reference the Durian.Core package as well.

Basics

The premise of this package is fairly straight-forward and recognizable. Similar to how System.AttributeUsageAttribute works, the Durian.InterfaceTargetsAttribute allows to specify what kind of members the target interface can be implemented by.

using Durian;

[InterfaceTargets(InterfaceTargets.Class)]
public interface ITest
{
}

// Success!
// ITest can be implemented, because ClassTest is a class.
public class ClassTest : ITest
{
}

// Error!
// ITest cannot be implemented, because StructTest is a struct, and ITest is valid only for classes.
public struct StructTest : ITest
{
}

It is possible to specify more than one member kind.

using Durian;

[InterfaceTargets(InterfaceTargets.Class | InterfaceTargets.Struct)]
public interface ITest
{
}

// Success!
// ITest can be implemented, because ClassTest is a class.
public class ClassTest : ITest
{
}

// Success!
// ITest can be implemented, because StructTest is a struct.
public struct StructTest : ITest
{
}

// Error!
// ITest cannot be implemented, because IInterfaceTest is an interface, and ITest is valid only for classes or structs.
public interface IInterfaceTest : ITest
{
}

Reflection

InterfaceTargets works only on syntax level - it is possible to implement an interface for a member of forbidden kind through reflection.

For cases when such behavior is the only intended way, InterfaceTargets.ReflectionOnly can be applied.

using Durian;

[InterfaceTargets(InterfaceTargets.ReflectionOnly)]
public interface ITest
{
}

// Error!
// ITest can be implemented in code.
public class ClassTest : ITest
{
}

// Error!
// ITest can be implemented in code.
public struct StructTest : ITest
{
}

Possible values

The possible values of the Durian.InterfaceTargets enum are:

• None - Interface cannot be implemented in code.
• ReflectionOnly - Interface can only be implemented through reflection; the same as None.
• Class - Interface can only be implemented by classes.
• Interface - Interface can only be implemented by other interfaces.
• Struct - Interface can only be implemented by structs.
• RecordClass - Interface can only be implemented by record classes.
• RecordStruct - Interface can only be implemented by record structs.
• All - Interface can be applied to all kinds of members; same as not specifying the Durian.InterfaceTargetsAttribute at all.

(Written by Piotr Stenke)