Creating dynamic instances by key

[silkfire]

I have the following scenario but am not sure how to solve it in Grace:

A service requires a dependency that is resolved with a string parameter sent to its constructor.

1. If the dependency has been resolved with this argument before, let Grace serve it (singleton),
2. If not, then create the dependency with the provided parameter and register is as singleton.

The argument is resolved dynamically from another dependency.

So is there a way in ExportFactory<DependencyProvidingDynamicArgument, IDependency> to cache instances by a dynamic key?

[ipjohnson]

There isn't something out of the box like that but I think it could be do able with a custom lifestyle. I'm assuming somewhere you would be doing

container.Locate<SomeType>(extraData: new { key = "SomeString"});

[ipjohnson]

Actually I forgot I do have something like this out of the box SingletonPerKey.

[silkfire]

@ipjohnson That's brilliant, huge thanks. Is the SingletonPerKey smart enough to not re-register the service if I provide it an already registered key?

If I run this:

container.Configure(c => c.Export<BasicService>().Lifestyle.SingletonPerKey((scope,context) => "A"));
container.Configure(c => c.Export<BasicService>().Lifestyle.SingletonPerKey((scope,context) => "A"));

Will it just silently ignore the second line?

[ipjohnson]

Sorry meant to reply to this yesterday and got side tracked. I think I might have misunderstood yesterday what you are looking for. Are you looking to do

• Keyed registration - multiple registrations of one or more types
• Keyed cached output - one registration that is then cached based on a key in the extra data provided at location time

The code you have there essentially will only return one instance because the function always returns "A".

[silkfire]

I was thinking a combination of both. Cache an instance based on a key (which is also a constructor argument to the type being resolved) that is different depending on what the func returns during runtime. Unless I'm getting confused here :)

[ipjohnson]

Hmmm ok well that could work, to answer your previous question the registration will just replace when you get one instance. If you get an enumeration of them you will get two.