Here is some code:
class Program
{
static void Main(string[] args)
{
MyClass class1 = new MyClass();
MyOtherClass class2 = new MyOtherClass();
Helper.UseAttribute<MyClass>(class1);
//Raise a warning to tell the developer that they cannot use this class
//as there is no property with the specified attribute.
Helper.UseAttribute<MyOtherClass>(class2);
}
}
public class MyAttribute : System.Attribute { }
class MyClass
{
[MyAttribute]
public string SomethingAwesome { get; set; }
}
class MyOtherClass
{
public string SomethingElseWhichIsAlsoPrettyAwesome { get; set; }
}
static class Helper
{
public static void UseAttribute<T>(T sender)
{
//Do something with the property that has MyAttribute
//If there isn't a property with this attribute, then raise
//a warning.
}
}
In an ideal scenario, I want to restrict a developer from passing classes to a method which do not have a certain attribute.
I am aware that I can use an interface, or a base class of some description, however the question really is whether something like the example above is possible.
If you're happy to either use the VS 2015 preview or wait until VS 2015 is out, you can use Roslyn for this.
You'd write a DiagnosticAnalyzer
class, probably registering a syntax node analyzer to specifically look for invocations of Helper.UseAttribute<T>
. When you find such a use, you'd find the symbol for T
and check whether there are any properties with the MyAttribute
attribute applied to it, and raise a warning if not. This warning will be shown in Visual Studio itself, as well as applying on CI builds (assuming you register the analyzer assembly appropriately).
It takes a while to get started with the Roslyn diagnostic APIs, but once you're used to it, it's really powerful.
Of course, another option is to throw an exception at execution time, and rely on there being unit tests around all callers so that you'd be able to catch it when they fail :) You should probably do that as well as adding compile-time support via Roslyn.
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