types.d.ts

types.d.ts

// https://www.typescriptlang.org/play?#code/JYOwLgpgTgZghgYwgAgILIN4ChnLgIwQC5kQBXAW32h2QBMIYSBnMKUAc1o4AtgTyVGrgBWAawA2JAEoQEAeyh0APK3YgOAGlKVqUAHy0KIeQN3QA2gF0sAXyxYA9ACpnyAPIgJAT2QcIYMgADlDyQdBgwBDMyDChFMgAKsgA7jzQKABucBJkKMAx8jDIYN7hyADSyM6OWKXlnj7KidoV+sgAvMgACsAIYs3a2LgW3cigyGIQ3kVJViSJo1bIEAAekCB0MVUA-D3IAhCZNLYWUzPFiVaGTo7IEsAUwIFg8sjyXr6CesGh4VCRaJ1MooABCnQ8n2UqG032gNwUIFYJWiYBI4K6wzwhBIAEYAEwAZk03D4JAALABWABsJPsQA

/** Only get properties from T where value is of type K */
type Only<T, K> = Pick<T, {
  [P in keyof T]: T[P] extends K ? P : never
}[keyof T]>

//
// Writable properties from an interface
//
type IfEquals<X, Y, A=X, B=never> =
  (<T>() => T extends X ? 1 : 2) extends
  (<T>() => T extends Y ? 1 : 2) ? A : B;

type WritableKeys<T> = {
  [P in keyof T]-?: IfEquals<{ [Q in P]: T[P] }, { -readonly [Q in P]: T[P] }, P>
}[keyof T];

// https://www.typescriptlang.org/play?#code/JYOwLgpgTgZghgYwgAgCoQM5mQbwFDLJQRwAmA9iADYCeycAXMiAK4C2ARtAch01lFABzPAF88eMDQAOKAJIwAogEcWcKhgA8ADQA0yAJr6AggF49yAEKmQEAG7QAfMlM8AFJtSO3AShfPUZAgAD0gQUgxkbWQAfmQARmQmACY-ELCI909vP1MAoNCIcMiDWISk5FSy4wrLAG4JKVlkAHVBMDgOKggAaQgaLS8XXB4AbQAFZFBkAGt+8hg0AF0AWhimBRU1DU0cZFGARSmQZHGlplQJpeRRfT2V4jJKWn2j6bOLq5v9cccxUbmNAWywakhkKDawA6XQg2WG42ACBmnn0kOh3T6A2yfzwCEoWHoTDRnW6nkwYGcphGhD4yAA5ABmOliIA
type Writable<T> = Pick<T, WritableKeys<T>>