• 含義

  可選命名引數:{param1,param2,…}

  可選位置引數:[param1,param2,…]

  如果存在具體引數，可選引數宣告，必須在引數後面

• 案例

void main(List<String> args) {
  printPerson("張三");
  printPerson("張三", age: 28);
  printPerson("張三", age: 28, gender: "huang");
  printPerson("張三", gender: "huang", age: 28);
  print("---------------------------------------------");
  printPerson2("張三");
  printPerson2("張三", 28);
  printPerson2("張三", 28, "huang");
}

// 可選命名引數(常用)
printPerson(String name, {int age, String gender}) {
  print("name=$name,age=$age,gender=$gender");
}

// 可選位置引數
printPerson2(String name, [int age, String gender]) {
  print("name=$name,age=$age,gender=$gender");
}

 

name=張三,age=null,gender=null
name=張三,age=28,gender=null
name=張三,age=28,gender=huang
name=張三,age=28,gender=huang
---------------------------------------------
name=張三,age=null,gender=null
name=張三,age=28,gender=null
name=張三,age=28,gender=huang
Exited