Utilizing a string as an index in TypeScript

Struggling with the following code snippet:

    interface IStudentType {
      [key: `${Students}`]: IStudent | IStudentMaths| IStudentPhysics
     }

The error message received is TS1268: An index signature parameter type must be 'string', 'number', 'symbol', or a template literal type.

To address this, an attempt was made:

type StudentCategories = 'Mature' | 'Graduate' | 'Fresher'

interface IStudentType {
  [key: `${StudentCategories}`]: IStudent | IStudentMaths| IStudentPhysics
}

TS1337: An index signature parameter type cannot be a literal type or generic type. Consider using a mapped object type instead.

Looking for suggestions on how to resolve this issue.

Answer №1

If you possess a combination of keys, the recommended approach is to utilize the Record feature.

type StudentCategories = 'Mature' | 'Graduate' | 'Fresher' // these categories are defined as keys in the dataset

type IStudent = {
    tag: 'IStudent '
}

type IStudentMaths = {
    tag: 'IStudentMaths'
}
type IStudentPhysics = {
    tag: 'IStudentPhysics'
}

type StudentType = Record<StudentCategories, IStudent | IStudentMaths | IStudentPhysics>

Interactive Code Playground

You can also explore using Symbol and Template String Pattern Index Signatures along with this Pull Request, but make sure to include a prefix:


interface StudentType {
    [prop: `${string}-${StudentCategories}`]: IStudent | IStudentMaths | IStudentPhysics
} 

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