@ ISA array and exporter in Perl

The inheritance of Perl classes (packages) is implemented through the @ ISA array. In short, Perl regards it as a special array of directory names, similar to the @ INC array (the @ INC array contains a reference path ). When Perl cannot find the required method in the current class (package), it will search for the classes listed in this array.

Whether it sounds abstract ...... I will release an example for your reference. I usually see many examples. @ ISA works with exporter.

Arithmetic. PM

Package arithmetic; use strict; Use exporter; # Use vars to predefine global variables # If use vars is not used, a global error is reported or our is used. # Of course, if you do not use strict, no error will be reported. Use vars QW (@ ISA @ export @ export_ OK % export_tags); # This is what we call. Assign the exproter value to @ ISA array @ ISA = QW (exporter); # default export symbol @ export = QW (add subtract); # export the symbol as required, that is, when using, you must specify QW () @ export_ OK = QW (multiply divide); # export marked with key-value symbols. The export elements in the array are, it must exist in @ export and @ export_ OK. % Export_tags = (SPEC => [QW (& add & subtract & multiply & divide)]); sub add {My ($ No1, $ NO2) = @_; my $ result; $ result = $ No1 + $ NO2; return $ result;} sub subtract {My ($ No1, $ NO2) =@_; my $ result; $ result = $ No1-$ NO2; return $ result;} sub multiply {My ($ No1, $ NO2) =@_; my $ result; $ result = $ No1 * $ NO2; return $ result;} sub divide {My ($ No1, $ NO2) =@_; my $ result; $ result = $ No1/$ NO2; return $ result;} 1;

The @ export array contains the default exported variables and function names, which are obtained when you use the package. The variables and functions in @ export_ OK are exported only when the use package in the program has special requirements.
The key-value pairs in % export_tags only allow the program to contain specific symbol groups listed in @ export and @ export_ OK.

Script. pl

#! /Usr/bin/perl-wuse strict; Use warnings; Use Arithmetic; # The Special Import mentioned above, that is, @ export_ OK # Use Arithmetic is a Use Arithmetic QW (multiply divide) that does not contain @ export_ OK; # It is imported as a key-value symbol ,! Add stands for the use of arithmetic QW (: spec! Add); print add (1, 2), "\ n"; print multiply (1, 2), "\ n"; print divide (4, 2), "\ n ";

In the preceding example, the @ ISA array is used. What is the significance of this example?

There are two types of modules: traditional and object-oriented.

The traditional style module imports and uses defined subroutines and variables for callers.

An Object-Oriented module called as a class.

Therefore, the module has two methods for its interface providers to use: Export symbols and class method calls.

This example belongs to the former.