Type Aliases with Const and Volatile

1#include <iostream>
2
3using Integer = int;
4using ConstInteger = const int;
5
6int main() {
7  Integer i{42};
8  ConstInteger ci{10};
9
10  // OK
11  i = 100; 
12
13  // Error: assignment of read-only variable ci
14  ci = 20;  
15
16  // This is equivalent to 'const int ci2{30};
17  const Integer ci2{30};
18  
19  // Error: assignment of read-only variable ci2
20  ci2 = 40; 
21}

1using IntPtr = int*;
2using ConstIntPtr = const int*;
3using IntConstPtr = int* const;
4
5int main() {
6  int value{42};
7  IntPtr p1{&value};
8  ConstIntPtr p2{&value};
9  IntConstPtr p3{&value};
10
11  *p1 = 10;  // OK 
12  
13  // Error: assignment of read-only location
14  *p2 = 20;  
15
16  *p3 = 30;  // OK 
17
18  int anotherValue{100};
19  p1 = &anotherValue;  // OK
20  p2 = &anotherValue;  // OK
21  
22  // Error: assignment of read-only variable 'p3'
23  p3 = &anotherValue;  
24}

1using Integer = int;
2
3int main() {
4  // Equivalent to const int ci{42};
5  const Integer ci{42};
6
7  // Equivalent to volatile int vi{10};
8  volatile Integer vi{10};
9
10  // Error: assignment of read-only variable 'ci'
11  ci = 100; 
12  
13  // OK, but compiler won't optimize access to 'vi'
14  vi = 20;
15}

1#include <iostream>
2#include <vector>
3
4template <typename T>
5using ConstRef = const T&;
6
7int main() {
8  std::vector<int> vec{1, 2, 3};
9
10  ConstRef<std::vector<int>> constVecRef = vec;
11
12  // Error: 'constVecRef' is read-only
13  constVecRef.push_back(4);
14
15  for (ConstRef<int> element : constVecRef) {
16    std::cout << element << ' ';
17  }
18}