Following my series from less known features of Modern C++.
I saw this post the other day and I agreed with all his reasoning why enum in TypeScript aren't safe. (Read this article for more information.)
To solve these problems C++ 11 introduces enum class or enum struct. If you are lazy to read that post then the old enum had the following problems:
- Conventional enums implicitly convert to int, causing errors when someone does not want an enumeration to act as an integer.
- Conventional enums export their enumerators to the surrounding scope, causing name clashes.
- The underlying type of an enum cannot be specified, causing confusion, compatibility problems, and makes forward declaration impossible.
Syntax
enum [class|struct] [identifier] [:type] {list};
Both class and struct have the same meaning here (for no damn reason).
Usage
#include <iostream>
enum struct Num {One, Two, Three, Four, Five}; // default type is int
int main() {
Num one = Num::One; // using :: operator for scope values
std::cout << static_cast<int>(one) << std::endl; // using static_cast to obtain the numerical value
auto match_enum = [](Num one) {
switch(one) {
case Num::One:
std::cout << "Num is one" << std::endl;
break;
case Num::Two:
std::cout << "Num is two" << std::endl;
break;
case Num::Three:
std::cout << "Num is one" << std::endl;
break;
default:
std::`ncout << "Invalid" << std::endl;
break;
}
};
match_enum(one); // Using Num::One
match_enum(Num(1)); // Casting the value to Num enum
}
```
Just like `enum` the values should be of literal type. There will be name clashes if we have `enum` and `enum class|struct` of the same name.
### `enum` V/S `enum class|struct`
- `enum` elements are accessed by `.` and `enum class|struct` are accessed by `::`.
- There can be clashes with other `enum` whereas `enum class|struct` are scoped so there are no clashes.
- `enum` can be converted into other `enum` but this isn't the case for `enum struct|class`.
```cpp
#include <iostream>
enum class Day {Mon, Tues, Wed, Thur, Fri, Sat, Sun};
//enum Day {Mon, Tues, Wed, Thur, Fri, Sat, Sun}; // Error : Previous defination at line 2
enum Days {Mon, Tues, Wed, Thur, Fri, Sat, Sun};
int main() {
Days day_scoped = Mon;
int num = day_scoped; // Enum converted into int
std::cout << num << std::endl;
Day days;
days = Day::Mon;
// int num2 = Day; // Error: Scoped Enum cannot be converted to int implicitly
int num_scoped = static_cast<int>(days); // Valid: Scoped Enum converted to int explicitly
std::cout << num_scoped << std::endl;
return 0;
}
```
If we un-commented the some code above then the program will raise errors.
### Code
All the code used in this article is available here.
{% github https://github.com/Delta456/modern_cpp_series %}
If there is some mistake or confusion then please tell me by commenting below!
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