Overloading of subroutines

In Mosel, it is possible to re-use the names of subroutines, provided that every version has a different number and/or types of parameters. This functionality is commonly referred to as overloading.

An example of an overloaded function in Mosel is getsol: if a variable is passed as a parameter it returns its solution value, if the parameter is a constraint the function returns the evaluation of the corresponding linear expression using the current solution.

Function abs (for obtaining the absolute value of a number) has different return types depending on the type of the input parameter: if an integer is input it returns an integer value, if it is called with a real value as input parameter it returns a real.

Function getcoeff is an example of a function that takes different numbers of parameters: if called with a single parameter (of type linctr) it returns the constant term of the input constraint, if a constraint and a variable are passed as parameters it returns the coefficient of the variable in the given constraint.

The user may define (additional) overloaded versions of any subroutines defined by Mosel as well as for his own functions and procedures. Note that it is not possible to overload a function with a procedure and vice versa.

Using the possibility to overload subroutines, we may rewrite the preceding example `Quick sort' as follows (model qsort2.mos).

model "Quick sort 2"

 parameters
  LIM=50
 end-parameters

 forward procedure qsort(L:array(range) of integer)

 declarations
  T:array(1..LIM) of integer
 end-declarations

 forall(i in 1..LIM) T(i):=round(.5+random*LIM)
 writeln(T)
 qsort(T)
 writeln(T)

 procedure swap(L:array(range) of integer,i,j:integer)
  (...)                        (same procedure body as in the preceding example)
 end-procedure

 procedure qsort(L:array(range) of integer,s,e:integer)
  (...)                        (same procedure body as in the preceding example)
 end-procedure

! Start of the sorting process
 procedure qsort(L:array(r:range) of integer)
  qsort(L,getfirst(r),getlast(r))
 end-procedure

end-model

The procedure qsort_start is now also called qsort. The procedure bearing this name in the first implementation keeps its name too; it has got two additional parameters which suffice to ensure that the right version of the procedure is called. To the contrary, it is not possible to give procedure swap the same name qsort because it takes exactly the same parameters as the original procedure qsort and hence it would not be possible to differentiate between these two procedures any more.