TypeScript type metadata symbols and interfaces

[remojansen]

I have some questions about the metadata symbols that are added by the TypeScript compiler to the generated JavaScript code when using the --emitDecoratorMetadata flag and decorators.

I'm aware of:

• "design:type" [The serialized form of the type of ?] the decorator target
• "design:paramtypes" [The serialized form of ?] the return type of the decorator target if it is a function type, undefined otherwise.
• "design:returntype" A list of [serialized ?] types of the decorator target’s arguments if it is a function type, undefined otherwise.

Is the "design:name" symbol is available?

• "design:name" The name of the decorator target

I'm hoping to find a symbol that will add the reflect-metadata that I need. I think I'm looking for something that is not available, something like design:implementedtypes or design:interfaces.

What I want to be able to do is be to get the names of the implemented interfaces.

@somedecorator
class Ninja implements INinja, IWarrior {
   // ...
}

The metadata that I would like to be added by the compiler is something would be something like the following:

Reflect.metadata("design:implementedtypes", ["INinja","IWarrior "]);

As an alternative (I don't know if that is the case) it would be OK for me if the "design:type" added the interfaces as well.

Reflect.metadata("design:type", ["Ninja", "INinja","IWarrior"]);

Also, are the serialized form of the types emitted?

reflect.metadata("design:type", ["Ninja"]);

or the actual types?

reflect.metadata("design:type", [Ninja]);

Thanks

[DanielRosenwasser]

Hey @remojansen, I'm not as familiar with decorators as some others on the team, but perhaps this comment may answer your question to some extent. If not, I can try to ping a few others from the team to help answer.

[remojansen]

@DanielRosenwasser thanks for the help.

I had a few questions and now I have some answers:

• Are strings used as the serialized forms of a type? No, and interfaces are serialized to Object.
• Also, are the serialized form of the types emitted? Yes but serialization does not work as I expected. If somebody reach this page wondering the same please note that the types are not serialized into strings.

But I still have some questions:

• Is the "design:name" symbol is available? This will return a string I assume?

And I would like to get more people to think about this issue because in the issue above (#2305) I see that @giancarloa said:

it all looks great EXCEPT the interfaces... don't you think it's a serious problem that there's no way to query metadata for interfaces? in my case for example I would never ever do the first example I gave above. Instead I would always do the second which is program against an interface.

Maybe more developer feel this way and we need to consider some solution. Maybe the solution is a new metadata symbols like the one I was making up in my original question "design:interfaces". I understand that you cannot return the interface as an object so maybe we instead of "design:interfaces" need string versions of all the currently available symbols, something like "design:stringified_type" which would generate ["Ninja", "INinja","IWarrior"] for

@somedecorator
class Ninja implements INinja, IWarrior {
   // ...
}

Thanks

[DanielRosenwasser]

Is the "design:name" symbol is available? This will return a string I assume?

The types of our decorators may help describe what you're interested in.

• For a property, you'll get the name of the property.
• For a method/accessor, you'll get the name of the method/accessor.
• For a parameter in a method/accessor, you'll get the name of the method/accessor.

@rbuckton can feel free to correct me.

Maybe more developer feel this way and we need to consider some solution.

I think the following #3015 (comment) is relevant.

[rbuckton]

@remojansen We are considering adding more type information. My current proposal can be found here.

[remojansen]

@rbuckton thanks for letting me know. I took a look to your proposal and I found what I need:

  /**
    * Implemented interfaces.
    */
  implements?: Type[];

Do you have an open issue / proposal somewhere that I can follow to keep an eye on the updates regarding this topic? If there is an open issue / proposal already we can close this issue.

Thanks

[DanielRosenwasser]

Hey @remojansen, I think the plan is to convert @rbuckton's proposal into a formal issue; not sure when we'll be doing that, so maybe we'll leave this open for now.

[mhegazy]

looks like this is already covered here: #3015 (comment)