如何使Dart对象/类可转位？ [英] How does one make a Dart object/class indexable?

问题描述

在Python中，我可以通过重写 __ getitem __ 使任何类支持索引：

  class Test：
 def __getitem __（self，key）：
 return self.data [key] 
  / pre> 
 
 
 Dart是否有类似的结构？
解决方案
假设 __ getitem __ 可以使用indexing语法（ object [index] ），允许您通过定义 operator [] 执行相同操作。示例：
  class Test {
 var data = {
a ：1，
b：2 
}; 
 
 operator []（index）=> data [index]; 
} 
 
 main（）{
 var t = new Test（）; 
 print（t [a]）; 
 print（t [b]）; 
} 
  
您还可以定义对 ] = ：
  class Test {
地图数据= {
a：1，
b：2 
}; 
 
 operator []（index）=> data [index]; 
 operator [] =（index，value）{data [index] = value; } 
} 
 
 main（）{
 var t = new Test（）; 
 print（t [a]）; 
 print（t [b]）; 
 t [c] = 3; 
 print（t [c]）; 
} 
  
 
In Python I can make any class support indexing by overriding __getitem__ like so:
class Test:
   def __getitem__(self, key):
      return self.data[key]
Does Dart have a similar construct for this?
解决方案
Assuming that the __getitem__ thing lets you use the "indexing" syntax (object[index]), yes, Dart lets you do the same by defining operator []. Example:
class Test {
  var data = {
    "a": 1,
    "b": 2
  };

  operator [](index) => data[index];
}

main() {
  var t = new Test();
  print(t["a"]);
  print(t["b"]);
}
You can also define the "opposite" operator []=:
class Test {
  Map data = {
    "a": 1,
    "b": 2
  };

  operator [](index) => data[index];
  operator []=(index, value) { data[index] = value; }
}

main() {
  var t = new Test();
  print(t["a"]);
  print(t["b"]);
  t["c"] = 3;
  print(t["c"]);
}


                        
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