SafeEnum< Target, LayoutType > Struct Template Reference

Helper class used to define safe enumerations. More...

#include <SafeEnum.h>

Detailed Description

template<typename Target, typename LayoutType = unsigned int>
struct ble::SafeEnum< Target, LayoutType >

Helper class used to define safe enumerations.

C++ 98 enums expose different security holes:

• Scope The scope of the enum is the scope defining it. In other words, enumerator defined at namespace scope are in the same scope that other enumerator defined in that namespace even if they belong to a different enumeration. As a result it is really easy to collide names between two different enumerators. At the end, the programmer has to protect its declaration with long prefixing.
• Unsafe comparison: enumerators really just are named integer and can be implicitly converted to integer. As a result it is possible to compare value of different enum type.
• Layout: The layout type of enumerations is implementation defined.

This template class expose a framework to overcome those issues:

First enum has to be defined in a structure which inherit from this class. The target type is the name of the structure containing the enumeration while LayoutType is the inner type used to stored the enum.

Comparison operator are provided so it is not possible to compare a SafeEnum of a type to another SafeEnum of a different type.

Implicit conversion to integer is not defined, users have to either use the value function which return the integer value stored in an EnumType. Client class can also define their own conversion operation.

Template Parameters:

Target	structure containing the enumeration definition.
LayoutType	Inner type used to store enumeration value.

    struct color_t : SafeEnum<color_t> {
        enum type {
            RED,
            GREEN,
            BLACK
        };

        color_t(type) : SafeEnum<color_t>(type) { }
    };

    // use an uint8_t to store the enumeration value
    struct shape_t : SafeEnum<shape_t, uint8_t> {
        enum type {
            RECTANGLE,
            CIRCLE,
            TRIANGLE
        };

        shape_t(type) : SafeEnum<shape_t>(type) { }
    };

    // shape enumerator is in the shape_t scope.
    shape_t shape = shape_t::RECTANGLE;

    shape_t shape = color_t::RED; // Compilation error

    if (shape == shape_t::CIRCLE) {
    }

    // compilation error
    if (shape == color_t::RED) {

    }

    void sink(shape_t); (1)
    void sink(color_t); (2)

    sink(shape); // use overload (1)
    sink(color); // use overload (2)

    // explicit access to the value is mandatory when a SafeEnum value is used
    // as the condition in a switch statement
    switch(shape.value()) {
        case shape_t::RECTANGLE:
            break;
    }

Definition at line 109 of file SafeEnum.h.

Constructor & Destructor Documentation

Member Function Documentation

Friends And Related Function Documentation