Use reflect-metadata to determine complex types when possible

[ms1111]

For non-primitive types we need to use @SerializeProperty({ fromJSONStrategy: toSerializable(SomeClass) }) to specify the type information.

There is actually some metadata injected by the TypeScript compiler that we could use to shorten this down to @SerializeProperty().

• users would have to install the reflect-metadata package if they want to use this feature
• they would also have to configure TypeScript to emitDecoratorMetadata and enable experimentalDecorators
• I've read that it won't work for circular references, so manual type specification would still be required sometimes
• it also doesn't work for arrays of non-primitive types
• the last two points are counterintuitive and surprising, and could lead to bugs in user code

Looking at another project, TypeORM it has a @Column() annotation that is kind of similar in purpose to our @SerializeProperty(). It's able to get the type info as long as users follow its installation instructions to install reflect-metadata.

References:

• https://spin.atomicobject.com/2017/04/24/typescript-modular-typesafe-metadata/
• https://medium.com/@aaltuj/reflect-metadata-and-the-missing-feature-working-with-typescript-decorators-be850c4ec9a4
• http://blog.wolksoftware.com/decorators-metadata-reflection-in-typescript-from-novice-to-expert-part-4#4-complex-types-serialization_1

May or may not be viable, but it looks cool.

[hardy925]

I definitely looked into this - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Reflect and https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/defineProperties

One of my first iterations tried to use reflection but we found the double indexed map to be better. It was also important for this to be zero-dependency (IDK why - but it is). IIRC we found that to do this we would need the decorator on the class, which is completely different from how property decorators work and we ran into issues with that approach as well.

That said, knowing that a property value type is Serializable is interesting.