Compile-time Constant Functions

nesC has a new kind of constant expression: constant functions. These are functions defined within

the language which evaluate to a constant at compile-time.

nesC currently has two constant functions:

•  unsigned  int  unique(char  *identifier)

Returns:  if the program contains n calls to unique with the same identifier string, each

calls returns a different unsigned integer in the range 0..n − 1.

The intended use of unique is for passing a unique integer to parameterised interface instances,

so that a component providing a parameterised interface can uniquely identify the various

components connected to that interface.

 

•  unsigned  int  uniqueCount(char  *identifier)

Returns:  if the program contains n calls to unique with the same identifier string, then

uniqueCount will return n.

The intended use of uniqueCount is for dimensioning arrays (or other data structures) which

will be indexed using the numbers returned by unique.  For instance, a Timer service that

identifies its clients (and hence each independent timer) via a parameterised interface and

unique can use uniqueCount to allocate the correct number of timer data structures.