refactor(ContextLoader): remove ClassLoader

[initial-wu]

ClassLoader does nothing but create itself. So why bother adding a new concept?

Checklist

• [x] npm test passes
• [x] commit message follows commit guidelines

Affected core subsystem(s)

ContextLoader

Description of change

• remove ClassLoader. Instead create a plain object named namespace in getIntance()

• use definePropertyGetter() to define getters for all service instances (e.g. b of service.a.b), serivce namespaces (e.g. a of service.a.b) and ctx.service itself

[codecov[bot]]

Codecov Report

Merging #185 into master will not change coverage. The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #185   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          19     19           
  Lines        1068   1055   -13     
=====================================
- Hits         1068   1055   -13

Impacted Files	Coverage Δ
lib/loader/context_loader.js	100% <100%> (ø)	:arrow_up:

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[popomore]

Will it improve performance? In my opinion, Class is more readable than function, so I don't think it need be changed.

[initial-wu]

Well, for me a new concept named ClassLoader is more confusing. When i just see the name without reading the details i guess it is similar to ContextLoader or FileLoader, and it should have a load() method. And a 'loader' is expected to work during boot, but the fact is that the ClassLoader is instantiated for a special ctx. The ClassLoader has no behavior but creating an object with some getters. In other words, it just provides a namespace. i think there is no need to declare a special ClassLoader. In addition, a getter named serivce on ctx and a getter named foo on ctx.service are similar inside. Both they lazily initialize a instance and cache it with a Map. So i could naturally use definePropertyGetter() to handle these. Thanks for more review and consideration.