Is there a way to specify object keys in alignment with a specific pattern that allows for a variety of different combinations

I am seeking a way to restrict an object to only contain keys that adhere to a specific pattern. The pattern I require is: "{integer}a+{integer}c". An example of how it would be structured is as follows:

{
    "2a+1c": {
        // ...
    }
}

Is there a method to guarantee that any new key added to this object complies with the defined pattern, without explicitly listing out all possible valid keys (as this is unfeasible)?

To provide further clarification on what I have in mind, here is an approach to ensuring an object only contains keys from an enum:

type ObjectWithEnumedKeys = {
  [key in TheEnum]?: number;
}

It's important to note that I am not interested in solutions involving logic such as methods within a class or closures to enforce these restrictions.

Answer №1

In the latest release of TypeScript 4.4, there is a new feature introduced called Template Literal Types in index signatures. These types allow for interpolation with any numbers, not just integers. While it may not be exactly what you are looking for, it comes very close:

type TheEnum = `${number}a+${number}c`;
type ObjectWithEnumedKeys = {
  [key in TheEnum]?: number;
}


const x: ObjectWithEnumedKeys = {
  "2a+1c": 3, // works as expected
  "5.5a+3.1c": 8.6, // accepted as well, hm
  "error": undefined, // complains that "property 'error' does not exist in type 'ObjectWithEnumedKeys'", as expected
}

(Demo in Playground)

String types validated by regex that would allow for specifying integer coefficients are currently being discussed.

Answer №2

Can an object be constrained to have keys that are only strings matching a specified Regular Expression?

Unfortunately, no.

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