How to fix Type parameter 'K' is not assignable to keyof any in TypeScript

// ❌ Error: K is not assignable to keyof any
function getProperty<T, K>(obj: T, key: K): T[K] {
  return obj[key];
}

// ✅ Fixed: K is constrained to be a key of T
function getProperty<T, K extends keyof T>(obj: T, key: K): T[K] {
  return obj[key];
}

// ❌ Error without constraint
type MyMappedType<K> = {
  [P in K]: string;
};

// ✅ Fixed: K must be a valid property key
type MyMappedType<K extends PropertyKey> = {
  [P in K]: string;
};

// Or equivalently using keyof any
type MyMappedType<K extends keyof any> = {
  [P in K]: string;
};

// Only allow string keys
function getStringProperty<T, K extends Extract<keyof T, string>>(
  obj: T,
  key: K
): T[K] {
  return obj[key];
}

// Or for general use
type StringKeyedObject<K extends string> = {
  [P in K]: any;
};

// ❌ Error: T not assignable to keyof any
type Getters<T> = {
  [K in T]: () => K;
};

// ✅ Fixed: T constrained to valid keys
type Getters<T extends PropertyKey> = {
  [K in T]: () => K;
};

// ✅ Better: Use with keyof to create getters for an object type
type ObjectGetters<T> = {
  [K in keyof T as `get${Capitalize<string & K>}`]: () => T[K];
};

// ❌ Error in Pick-like utility
type MyPick<T, K> = {
  [P in K]: T[P];
};

// ✅ Fixed with proper constraint
type MyPick<T, K extends keyof T> = {
  [P in K]: T[P];
};

// Usage
interface User {
  id: number;
  name: string;
  email: string;
}

type UserPreview = MyPick<User, 'id' | 'name'>; // Works!

// ❌ Common mistake in accessor functions
function setValue<T, K>(obj: T, key: K, value: any): void {
  obj[key] = value; // Error: K not assignable to keyof any
}

// ✅ Fixed with constraint and proper typing
function setValue<T, K extends keyof T>(
  obj: T,
  key: K,
  value: T[K]
): void {
  obj[key] = value;
}

// ✅ Alternative: Use Record type
function setValue<K extends string>(
  obj: Record<K, any>,
  key: K,
  value: any
): void {
  obj[key] = value;
}