Item 39: Prefer Unifying Types to Modeling Differences

要点

• Having distinct variants of the same type creates cognitive overhead and requires lots of conversion code.
• Rather than modeling slight variations on a type in your code, try to eliminate the variation so that you can unify to a single type.
• Unifying types may require some adjustments to runtime code.
• If the types aren't in your control, you may need to model the variations.
• Don't unify types that aren't representing the same thing.
• 相同类型的不同变体会增加认知负担，并需要大量的转换代码。
• 与其在代码中建模类型的轻微变化，不如消除这些变化，以便将它们统一为单一类型。
• 统一类型可能需要对运行时代码进行一些调整。
• 如果这些类型不在你的控制之下，可能需要对变体进行建模。
• 不要统一那些不代表相同事物的类型。

正文

interface StudentTable {
  first_name: string
  last_name: string
  birth_date: string
}

💻 playground

---

interface Student {
  firstName: string
  lastName: string
  birthDate: string
}

💻 playground

---

type Student = ObjectToCamel<StudentTable>
//   ^? type Student = {
//        firstName: string;
//        lastName: string;
//        birthDate: string;
//      }

💻 playground

---

async function writeStudentToDb(student: Student) {
  await writeRowToDb(db, 'students', student)
  //                                 ~~~~~~~
  // Type 'Student' is not assignable to parameter of type 'StudentTable'.
}

💻 playground

---

async function writeStudentToDb(student: Student) {
  await writeRowToDb(db, 'students', objectToSnake(student)) // ok
}

💻 playground