Constraints are not allowed on non-generic declarations

Question

I've had a look at the other similar questions but the issues were syntax errors. Perhaps I'm missing something but my syntax looks correct as far as I can tell. I'm trying to declare a method as follows:

internal IDictionary<string, T> FillObjects(
    IReadableRange<T> svc,
    Func<T, string> getKey) where T : BaseEntity
{
}

but am getting the compiler error:

constraints are not allowed on non-generic declarations

any ideas?

thanks

Matt

Answer 1

The problem is that your method does not define the generic type <T>. It just uses the type T given by the enclosing type.

And you can declare constraints only at the same place where you define generic parameters.

There are two solutions:

1., You should either define generic parameters on the function:

public class EnclosingType
{
    internal IDictionary<string, T> FillObjects<T>(
        IReadableRange<T> svc,
        Func<T, string> getKey) where T : BaseEntity
    {
    }
}

In your case it doesn't compile, because you EnclosingType is probably the EnclosingType<T> that leads to an ambiguity between EnclosingType's T and FillObjects' T:

2., Or you could just define the constraints on the enclosing type:

public class EnclosingType<T>
    where T : BaseEntity
{
    internal IDictionary<string, T> FillObjects(
         IReadableRange<T> svc,
         Func<T, string> getKey)
    {
    }
}