refactor(cwl): Change implementation of LiveTailRegistry to standard map

[keeganirby]

Problem

The nestedMap implementation of the registry was forcing a defined Default item. This doesn't fit the usecase I am aiming to provide by this registry. There is no default object to be returned. If an item doesn't exist in the registry, we should handle an undefined object, and not a placeholder. In other words, there is no concept of a placeholder/default value for a LiveTailSession.

Additionally, set on the NestedMap would perform a deep merge. I am wanting to replace the object.

Originally I defined the default object to an exception, but the NestedMap set operation calls get. And if there isn't already a value in the map, it would throw the exception defined as the default object. This means we could never add any item to the map.

Solution

Swap the underlying implementation of the registry to a basic Map.
I am still defining a LiveTailSessionRegistry class so we can statically initialize a registry singleton, as well as leaving the possibility open to override or extend the Map class. Also so we can pass around the type LiveTailSessionRegistry instead of Map<Foo, Bar>.

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License: I confirm that my contribution is made under the terms of the Apache 2.0 license.

[justinmk3]

Thanks for the clear explanation!