Typescript: Why not use string-literal types to represent enums of type string?

[bedag-moo]

Description

The typescript-angular2 generator currently emits enums in the form

    export enum StatusEnum {
        Open = <any> 'open',
        InProgress = <any> 'inProgress',
        Resolved = <any> 'resolved',
        Closed = <any> 'closed'
    }

For enums of type string the translation

    type StatusEnum = "open" | "inProgress" | "resolved" | "closed";

would be more type-safe (witness #5146), and more flexible to use. For instance, I could do:

    const badgeType: {[K: StatusEnum]: string} = {
        open: "danger",
        inProgress: "warning",
        resolved: "info",
        closed: "success",
    }

rather than

    const badgeType = <any>{}; // no type safety, because I can not enumerate the enum values
    badgeType[StatusEnum.Open] = "danger";
    badgeType[StatusEnum.InProgress] = "warning";
    badgeType[StatusEnum.Resolved] = "info";
    badgeType[StatusEnum.Closed] = "success";

as well as directly refer to enum constants in an angular template:

<div [ngSwitch]="issue.state">
  <div *ngSwitchCase="'open'"> 

rather than an unnecessary indirection in the template

<div [ngSwitch]="issue.state">
  <div *ngSwitchCase="StatusEnum.Open"> 

over the component

import { StatusEnum} from ...

export class MyComponent {
  StatusEnum = StatusEnum;
}

to the imported enum.

Swagger-codegen version

master

Suggest a fix/enhancement

Generate enums of type string as union of string literals, leaving enums of numeric type as they are (they need special treatment anyway to fix #3500).

[bedag-moo]

If everyone is ok with the change, I can submit a PR.

[bedag-moo]

I just came across yet another reason for this change: If the same enumeration is used by two properties, the code generator emits separate enums, which aren't mutually assignable. If a union of string literals were used instead, the typescript compiler would verify structural equality, and permit the assignment.