如何在Dart 2.2之后设置文字 [英] How to set literals after Dart 2.2

问题描述

直到2.2，如何在Dart 2.2之后设置文字才支持Set文字.请随意发表评论.谢谢.

Set literals were not supported until 2.2, How to set literals after Dart 2.2. Please feel free to comment. Thank you.

class item_t {
  String name;
  int weight;
  int value;
}

main() {
  const List<item_t> items = [
    {'map', 9, 1}, // reports errors
  ];
}

更新1

我可以将列表定义为一系列的define语句.但是，这似乎无效.

I could define the list as a serial of define statements. However, it seems it is ineffective.

class item_t {
  String name;
  int weight;
  int value;
}

main() {
  // final item_t items = new item_t(100);
  List<item_t> items = new List(2);

  items[0].name = 'map';
  items[0].weight = 9;
  items[0].value = 1;

}

在C语言中，我可以有效地定义结构，但我不知道如何在dart中实现.

In C language, I can define a structure effectively but I don't know how to do that in dart.

typedef struct {
    char *name;
    int weight;
    int value;
} item_t;

item_t items[] = {
    {"map",                      9,   150},
    {"compass",                 13,    35},
    {"water",                  153,   200},
};

更新2

谢谢jamesdlin的建议，我可以简化列表初始化并按索引访问元素.但是，它仍然不能像C语言一样有效.

Thank you jamesdlin's advise, I can simplify the list initialization and access the element by index. However, it still can't be as effective as C language.

 var mySet = [
    {"map", 9, 150},
    {"compass", 13, 35},
    {"water", 153, 200},
    {"sandwich", 50, 160},
    {"glucose", 15, 60},
    {"tin", 68, 45},
    {"banana", 27, 60},
    {"apple", 39, 40},
    {"cheese", 23, 30},
    {"beer", 52, 10},
    {"suntan cream", 11, 70},
    {"camera", 32, 30},
    {"T-shirt", 24, 15},
    {"trousers", 48, 10},
    {"umbrella", 73, 40},
    {"waterproof trousers", 42, 70},
    {"waterproof overclothes", 43, 75},
    {"note-case", 22, 80},
    {"sunglasses", 7, 20},
    {"towel", 18, 12},
    {"socks", 4, 50},
    {"book", 30, 10}
  ];

  print(mySet[0].elementAt(1));

推荐答案

您使用{和}来指定Set(和Map)文字:

You use { and } to specify Set (and Map) literals:

var mySet = {1, 2, 3};

请注意，为避免与Map文字产生歧义，创建空集时必须明确指定类型.例如:

Note that to avoid ambiguity with Map literals, you must explicitly specify a type when creating an empty set. For example:

var emptySet = <int>{};

另请参见 https://dart.dev/guides/language/language-tour#设置

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