C++ 返回具有常量成员变量的对象——赋值运算符被隐式删除

Question

struct MyStruct {
   const int a, b; 
   MyStruct(int a, int b): a(a), b(b) {}
}

map<int, MyStruct> m; 

m[2] = MyStruct(3, 4); // this would fail. Of course I can use m.insert( .... )
MyStruct t = m[2]; // this would not compile, because there is no assignment operator. 

我会得到下面的编译错误。

[assignment operator] is implicitly deleted because the default definition would be ill-formed:

如何解决这个问题？我想有常量成员变量，避免以后意外修改

Answer 1

有一个自动生成的复制构造函数，相当于

MyStruct(MyStruct &s): a(s.a), b(s.b) {}

使用它来创建拷贝:

MyStruct t(m[2]);