Type intersections using any

by

In TypeScript, any is an escape hatch from the type system. Or maybe a black hole that eats up every other type it touches. It is treated both as a top type (any value can be assigned to a variable of type any) and a bottom type (a value of type any can be assigned to a variable of any type). You might even say it is both a supertype of string and a subtype of string. That’s generally unsound; all types become assignable to all other types if you use any, but it’s a useful way to opt out of the type system and make assignments that the compiler would otherwise prevent.

If you want a real top type which isn’t a black hole, use unknown. You already know that never is the real bottom type. For more interesting reading on this, see Microsoft/TypeScript#9999.

For your code, try:

type PropertyMap = {
    prop1: {
        name: "somename";
        required: unknown; // top type
    };
    prop2: {
        name: "someothername";
        required: never; // bottom type
    }
}

type RequiredOnly = {
    [P in keyof PropertyMap]: PropertyMap[P] & PropertyMap[P]["required"]
}

Now RequiredOnly["prop1"] should act like what you want.

Hope that helps; good luck!

Any help appreciated.

I see what you did there.

More Related Contents:

  1. Difference between extending and intersecting interfaces in TypeScript?
  2. Typescript: understanding union and Intersection types
  3. Create a global variable in TypeScript
  4. Way to tell TypeScript compiler Array.prototype.filter removes certain types from an array?
  5. Difference between Variance, Covariance, Contravariance and Bivariance in TypeScript
  6. How to use fetch in TypeScript
  7. Typescript property does not exist on union type
  8. Typescript primitive types: any difference between the types “number” and “Number” (is TSC case-insensitive)?
  9. Specify method’s type without converting the method to property
  10. How to watch and reload ts-node when TypeScript files change
  11. Angular 2 View will not update after variable change in subscribe
  12. Can’t import CSS/SCSS modules. TypeScript says “Cannot Find Module”
  13. Changing Property Name in Typescript Mapped Type
  14. Type for “every possible string value except …”
  15. How to combine known interface properties with a custom index signature?
  16. Call a global variable inside module
  17. Obtaining the return type of a function
  18. tsc throws `TS2307: Cannot find module` for a local file
  19. Merge Two Interfaces
  20. What does the pipe(|) mean in typescript?
  21. Integrating Material Design Lite with Angular2
  22. Setting default value for TypeScript object passed as argument
  23. ts-node ignores d.ts files while tsc successfully compiles the project
  24. Typescript: accessing an array element does not account for the possibility of undefined return values
  25. What does enclosing a class in angle brackets “” mean in TypeScript?
  26. What’s the difference between ‘extends’ and ‘implements’ in TypeScript
  27. How to get argument types from function in Typescript [duplicate]
  28. typings vs @types NPM scope
  29. Self-referencing return type for static methods in inheriting classes
  30. How to place a dynamic component in a container

Leave a Comment