type_def

Typesafe typedefs

A method of declaring types that are strongly typesafe.

Avoids the problem of inadvertently mixing different typedef'd types.

The problem

Typdefs do not give you a lot of type safety, allowing the following runtime errors to occur.

typedef int event_t;

typedef int action_t;

void DoEvent(event_t event, action_t action)

{

...

event_t evt = action; // Oops! Runtime error. :-(

int e = event;

int a = action;

...

e = a; // Oops! Runtime error. :-(

}

event_t event = 1;

action_t action = 2;

DoEvent(action, event); // Oops! Runtime error. :-(

ETL typedefs are strongly typed and will not allow the errors above to be compiled.

#include "type_def.h"

ETL_TYPEDEF(int, event_t);

ETL_TYPEDEF(int, action_t);

void DoEvent(event_t event, action_t action)

{

...

event_t evt = action; // Compile time error. :-)

int e = event; // Implicit conversion to underlying type.

int a = action; // Implicit conversion to underlying type.

...

e = a; // Compile time error. :-)

}

event_t event = 1; // Implicit construction from underlying type.

action_t action = 2; // Implicit construction from underlying type.

DoEvent(action, event); // Compile time error. :-)

The class defines two class types; value_type which represents the underlying type and id_type that represents the

typedef unique type id.

The class defines all of the operators that the underlying type may be expected to support.

Also the class defines two get() member functions that return a const or non-const reference to the internal value, for

data binding purposes.

T& get()

const T& get() const

type_def.h