ConstrainedTypes

This library allows definition of range constrained subtypes of integral types.

It is similar to what is provided by Ada's range keyword.

Using this library, it is possible define a new type which can store values from a range. Assigning a value to a variable of this type will cause the value to be checked for validity. If it is outside the valid range, an exception will be raised.

These "automatic assertions" increase type safety of programs and help catching bugs early.

Example

#include "subtype_range_constrained.h"

typedef ct::RangeConstrained<short, 1, 12> month_t;

int main(void) {
    month_t m = 1; // OK
    m = 12; // OK
    m  = 13; // Exception!
    return 0;
}

Features

• Any integral type can be used including char and enumerations.
• Subtypes has full compatibility with their underlying type.
• Subtypes has the same memory representation as their underlying type.
• Range checking is performed only during assignment.
• Simple implementation and extensive test suite.

Use Cases

• Sub-type of char that represents only the lower case letters.

  typedef ct::RangeConstrained<char, 'a', 'z'> lower_alpha_t;

• Assuring that variables that supposed to store enums are not assigned a value which is not in the range of representable values for that enum. Note that there are sanitizers that will perform compile time check for this behavior. For example UBSan's -fsanitize=enum.

  enum color_enum {RED = 0, GREEN = 1, BLUE = 2};
  typedef ct::RangeConstrained<color_enum, RED, BLUE> Color;
  void setBackground(Color color);
  ...
  setBackground(3); // Exception!

• Physical quantities like speed or altitude have intrinsic constrains. Thus out of range value is an indication of a bug.

  typedef ct::RangeConstrained<int32_t, -2000, 100000> AltitudeFeetAboveSeaLevel;

• Values that represent quantity or count:

  ct::RangeConstrained<uint8_t, 0, 5> occupiedSeats;
  occupiedSeats = 7; // Exception!

• Indexes passed to a function. Note that for checking out of bounds access to arrays it is possible to use vectors.

  #define STATIONS 8
  ct::RangeConstrained<uint8_t, 0, STATIONS - 1> StationID;
  Data * getData(StationID stationID);
  ...
  Data *data = getData(8); // Exception!

Handling the Exception

#include <iostream>
#include "subtype_range_constrained.h"

typedef ct::RangeConstrained<short, 1, 12> month_t;

int main(void) {
    try {
        month_t m = 13; 
    } catch(const month_t::constraint_error& e) {
        std::cerr << e.what() << '\n';
        std::cerr << e.getFirst() << '\n';
        std::cerr << e.getLast() << '\n';
        std::cerr << e.getVal() << '\n';
    }
    return 0;
}