Passing Arrays to Functions

In the last section, we saw how the collapsing of function arguments into the single array @_ was a very useful feature, since it allowed us to call a function which operates on multiple values by either passing those values as a list, or simply passing them individually. When you really do want to pass an array to a function, however, this collapsing can prove very frustrating.

In the special case where you wish to pass a number of scalars and exactly one array to a function, you can take advantage of a property we first saw in Section 2.4. When you ``unroll'' an array into a literal list, if a member of the literal list is an array, it will grab all the remaining elements from the original array. By extracting the arguments from @_ into a call to my, we can pass exactly one array, given as the final argument, into our function. (For the ``official'' way of passing multiple arguments, using references, see the next section.)

Suppose we wish to write a program that will take as its arguments a tax rate and an array of prices, and which will return an array of taxes corresponding to the prices. By making the tax rate the first argument to the function, we can use the technique outlined above to catch the remaining arguments into an array.

     sub do_taxes{
         my($rate,@prices) = @_;
         my(@taxes);
         foreach $p (@prices){
             push(@taxes,$p * $rate);
         }
         return(@taxes);
     }