“列表名称”和“列表”有什么区别<String> Dart 中的名字”？

Question

What is the difference between the following two statements:

List names = ["John", "Robert", "James"];

List<String> names = ["John", "Robert", "James"];

Answer 1

Dart will in the first example assume the type should be List<dynamic> since you have just told the type system that you want a List without any specific restrictions.

In the second example, the created list are getting the type List<String> since you have provided a restriction of the type of elements you want in the list.

Another example would be the following:

var names = ["John", "Robert", "James"]; // or final instead of var

Here we are letting Dart automatically determine the most restrictive type possible. In this case, the names are going to be automatically typed List<String> .

You can see this if you print the runtimeType of each declared list:

void main() {
  List names1 = ["John", "Robert", "James"];
  print(names1.runtimeType); // List<dynamic>
  
  List<String> names2 = ["John", "Robert", "James"];
  print(names2.runtimeType); // List<String>
  
  var names3 = ["John", "Robert", "James"];
  print(names3.runtimeType); // List<String>
}