Question

I have an exe referencing a dll.

In the dll there’s some methods, the two we’re interested in are:

private static CacheItemPolicy _policy = new CacheItemPolicy();

[MethodImpl(MethodImplOptions.NoInlining)]
public static void SetValue(string Key, object Value)
{
    SetValue(Key, Value, _policy);
}

[MethodImpl(MethodImplOptions.NoInlining)]
public static void SetValue(string Key, object Value, TimeSpan TTL)
{
    SetValue(Key, Value, GetPolicy(TTL));
}

[MethodImpl(MethodImplOptions.NoInlining)]
private static CacheItemPolicy GetPolicy(TimeSpan TTL)
{
    return new CacheItemPolicy()
    {
        SlidingExpiration = TTL
    };
}

In my exe when I try to call this method: using just cache.SetValue(key, item); it compiles and works fine, but when called using cache.SetValue(key, item, new TimeSpan(0, 1, 0)); I get the following exception:

Error 1 The type ‘System.Runtime.Caching.CacheItemPolicy’ is defined in an assembly that is not referenced. You must add a reference to assembly ‘System.Runtime.Caching, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a’.

Why does the compiler say that I need to add this reference to an assembly that I’m not directly using in my code at this point?

I’m sure it’s something simple that I’m missing. I looked at Why do I need to reference a dll which I'm not using directly? but it refers to interfaces and that is not the case here.

Edit: there is also this:

protected static void SetValue(string Key, object Value, CacheItemPolicy Policy)
{
    // work is done here
}

But that’s protected and shouldn’t be visible to the calling exe.

Edit2: when this above SetValue that takes a CacheItemPolicy is set to private or internal, it works, why does protected (and protected internal) cause it to require the assembly?

Answer 1

Since that static SetValue is protected, it’s visible to derived classes.

So, if you can derive from the class (i.e. it’s public), then there’s a chance you could derive and use that method, meaning the reference is required.