Dart支持==表示平等，identical(a, b)表示身份.Dart不再支持===语法.
如果要判断对象是否"相等"，请使用==表示相等.您可以在类中实现==方法来定义相等的含义.例如:
class Person {
String ssn;
String name;
Person(this.ssn, this.name);
// Define that two persons are equal if their SSNs are equal
bool operator ==(other) {
return (other is Person && other.ssn == ssn);
}
}
main() {
var bob = Person('111', 'Bob');
var robert = Person('111', 'Robert');
print(bob == robert); // true
print(identical(bob, robert)); // false, because these are two different instances
}
请注意，a == b的语义是:
a或b是null，则返回identical(a, b)a.==(b)使用identical(a, b)判断两个变量是否引用同一实例.identical是dart:core中的顶级函数.