I am trying to create my own module in perl that provides functions for data analysis out of a database.
I have several functions in EDL::Functions, eg. EDL::Functions::Average.
package EDL::Functions;
use warnings;
use strict;
package EDL::Functions::Average;
use parent "EDL::Functions";
sub new{...}
sub execute {...}
1) What do i have to add so use EDL::Functions; automatically imports all modules in EDL::Functions? Currently i have to import all submodules (in EDL::Functions)in order to make it work:
BEGIN {
our $VERSION = 5.20;
use EDL::Functions::Average;
use EDL::Functions::GetAllValues;
use EDL::Functions::GetValueStart;
use EDL::Functions::GetValueEnd;
use EDL::Functions::Min;
use EDL::Functions::Max;
use EDL::Functions::Median;
}
2) I want to make sure that if someone else builds his own function module the compilation will fail if it doesn't have the functions new and execute. How can i achieve that?
Thanks for your help!
It should work
perl -I ./ -MEDL::Functions -e 'EDL::Functions::Average->new();'
returns "I'm new".
cat EDL/Functions.pm
package EDL::Functions;
use warnings;
use strict;
package EDL::Functions::Average;
use parent "EDL::Functions";
sub new{ print "I'm new"; }
sub execute { print "Executing something";}
1;
But I prefere different structure, not declare several packages in one pm file. It'll save time for other devs and follows common practice, so EDL::Functions::Average should be at EDL/Functions/Average.pm
Related
Is it possible to create global functions available across all namespaces like perl built-in functions?
First of all, "function" is the name given to Perl's named list operators, named unary operators and named nullary operators. They are visible everywhere because they are operators, just like ,, && and +. Subs aren't operators.
Second of all, you ask how to create a global sub, but all subs are already global (visible from everywhere) in Perl! You simply need to quality the name of the sub with the package if it's not in the current package. For example, Foo::mysub() will call my_sub found in package Foo from anywhere.
But maybe you want to be able to say mysub() instead of Foo::mysub() from everywhere, and that's a very bad idea. It violates core principles of good programming. The number of types of problems it can cause are too numerous to list.
There is a middle ground. A better solution is to create a sub that can be imported into the namespaces you want. For example, say you had the module
package Foo;
use Exporter qw( import );
our #EXPORT_OK = qw( my_sub );
our %TAGS = ( ALL => \#EXPORT_OK );
sub my_sub { ... }
1;
Then, you can use
use Foo qw( my_sub );
to load the module (if it hasn't already been loaded) and create my_sub in the current package. This allows it to call the sub as my_sub() from the package into which it was imported.
There is nothing simple that would allow one to somehow "register" user's subs with the interpreter, or some such, so that you could run them as builtins in any part of the program.
One way to get the behavior you ask for is to directly write to symbol tables of loaded modules. This has to be done after the modules have been loaded, and after subs that you add to those modules have been defined. I use INIT block in the example below.
Note that this has a number of weaknesses and just in general the idea itself is suspect to me, akin to extending the interpreter. Altogether I'd much rather write a module with all such subs and use standard approaches for good program design to have that module loaded where it needs to go.
Having said that, here is a basic demo
use warnings;
use strict;
use feature 'say';
use Data::Dump qw(dd pp);
use TestMod qw(modsub);
sub t_main { say "In t_main(), from ", __PACKAGE__ }
modsub("Calling from main::");
INIT {
no strict 'refs';
foreach my $pkg (qw(TestMod)) {
*{ $pkg . '::' . 'sub_from_main' } = \&t_main;
}
dd \%TestMod::;
}
This copies the reference to t_main from the current package (main::) into the symbol table of $pkg, under the name of sub_from_main, which can then be used with that name in that package.
For simplicity the name of the module is hardcoded, but you can use %INC instead, and whatever other clues you have, to figure out what loaded modules' stashes to add to.
The benefactor (or the victim?) module TestMod.pm
package TestMod;
use warnings;
use strict;
use feature 'say';
use Exporter qw(import);
our #EXPORT_OK = qw(modsub);
sub modsub {
say "In module ", __PACKAGE__, ", args: #_";
say "Call a sub pushed into this namespace: ";
sub_from_main();
}
1;
The name of the added sub can be passed to modules as they're loaded, instead of being hardcoded, in which case you need to write their import sub instead of borrowing the Exporter's one.
There are also modules that allow one to add keywords, but that's no light alternative.
The answer seems to be no, but you can impliment most of the behaivior that you want by using the symbol table *main::main:: to define a subroutine in all the namespaces.
use strict;
use warnings;
use Data::Dump qw(dd);
my $xx = *main::main::;
package A;
sub test {
printf "A::%s\n", &the_global;
}
package B;
sub the_global
{
"This is B::the_global";
}
sub test {
printf "B::%s\n", &the_global;
}
package main;
my $global_sub = sub { "The Global thing" };
for my $NS (keys %$xx) {
if ($NS =~ /^[A-Z]::$/) {
my $x = $NS . 'the_global';
if (defined &$x) {
printf "Skipping &%s\n", $x;
} else {
printf "Adding &%s\n", $x;
no strict 'refs';
*$x = $global_sub;
}
}
}
A::test;
This will not work on packages that are not referenced at all before the for loop above is run. But this would only happen if a require, use or package was eval'd after the code started running.
This is also still a compiler issue! You either need to refer to the global function as the_global() or &the_global if you are (as you should be) using use strict.
Sorry for my late response and thank you all for yours detailed answers and explanations.
Well.. I understood the right answer is: IT'S NOT POSSIBLE!
I'm mantaining a Perl framework used by some customers, and that framework exports some specialized subs (logging, event handling, controllers for hardware devices, domain specific subs and so). That's why I tried to figure out how to prevent the developers from importing my subs in all their packages.
I have a set of tests, always named Module.t, each one starts like this:
use 5.026;
use strict;
use warnings;
use Test::Perl::Critic (-severity => 3);
use Module::Path 'module_path';
use Test::More tests => 8;
use Test::Log4perl;
Test::Log4perl->suppress_logging;
BEGIN { use_ok("My::Module") }
critic_ok(module_path("My::Module"));
... actual tests for this module ...
It's done this way because a bunch of modules are not coded very nicely and in effort to refactor stuff as we go, I'm trying to write tests for individual modules over time. Eg. I can't just enable Perl::Critic for all sources cause it will blow up in my face.
I would like to ideally make a "parent" test for all of these so that when me or a different developer wants to write a new test they will always have all the required stuff. Something like:
use 5.026;
use strict;
use warnings;
# 6 tests because 2 (use_ok and critic_ok) are already in the parent
use parent ParentTest("My::Module", tests => 6);
... actual tests for this module ...
Does perl have a way of doing that?
Disclaimer: I'm a perl noob, so maybe this has a better solution :-)
Sounds like you just want a helper module that loads some other modules and runs some initial tests for you.
Something like:
# ParentTest.pm
package ParentTest;
use strict;
use warnings;
use Test::Perl::Critic (-severity => 3);
use Module::Path 'module_path';
use Test::More;
use Test::Log4perl;
sub import {
my (undef, $module, %args) = #_;
$args{tests} += 2;
plan %args;
Test::Log4perl->suppress_logging;
use_ok $module;
critic_ok module_path $module;
#_ = 'Test::More';
goto +Test::More->can('import');
}
1
Usage would be:
use ParentTest "My::Module", tests => 6;
This is all untested, but the idea is:
We want to run some code to set up the initial test plan and run some tests.
We also want to export everything that Test::More exports, so our caller doesn't have to use Test::More themselves.
use Some::Module #args is equivalent to BEGIN { require "Some/Module.pm"; Some::Module->import(#args); }, so we can just put our custom logic in the import method.
We start by ignoring the first argument (which is a class name because import is called as a class method) and assigning the remaining arguments to $module and %args.
We increment $args{tests} by 2 to account for the two extra tests we perform automatically (if tests wasn't passed in, it is implicitly created here).
We pass %args to plan from Test::More, which is nice for setting up a test plan outside of the initial use line.
We perform the initial tests.
We tail call Test::More::import, erasing our own stack frame. This makes it look like our caller did Test::More->import(), which exports all the Test::More utility functions to them.
The unary + in goto +Test::More->... has no real effect, but it helps distinguish between the goto LABEL and goto EXPRESSION syntactic forms. We want the latter interpretation.
This question already has answers here:
Perl - Package/Module Issues
(4 answers)
Closed 9 years ago.
I am trying to do simple module usage in Perl:
Flame/Text.pm:
package Flame::Text;
sub words { … }
1;
Flame/Query.pm:
package Flame::Query;
use Flame::Text qw(words);
sub parse_query { words(shift); }
parse_query 'hi';
1;
Why am I getting the following error message?
Undefined subroutine &Flame::Query::words called at Flame/Query.pm line 3.
The following works just fine:
package Flame::Query;
use Flame::Text;
sub parse_query { Flame::Text::words(shift); }
parse_query 'hi';
1;
You never imported or exported the words subroutine from the Flame::Text package. A statement use Some::Module #args is equivalent to:
BEGIN {
require Some::Module;
Some::Module->import(#args);
}
that is, the import method is called with the specified arguments. This method would usually export various symbols from one package into the calling package.
Don't write your own import, rather you can inherit one from the Exporter module. This module is configured by storing exportable symbols in the #EXPORT_OK global variable. So your code would become:
package Flame::Text;
use parent 'Exporter'; # inherit from Exporter
our #EXPORT_OK = qw/words/; # list all subs which you want to export upon request
sub words { ... }
Now, use Flame::Text 'words' will work as expected.
You need to do something like this
package Flame::Text;
use Exporter 'import'; # gives you Exporter's import() method directly
#EXPORT_OK = qw(words); # symbols to export on request
as perl doesn't export (or pollute) the namespace by default
http://perldoc.perl.org/Exporter.html
don't forget to
use strict; use warnings;
in all things perl
this is my first foray into subclassing with perl and I am wondering why I am getting this simple error...
"Can't locate object method "prepare" via package "WebDB::st" at /home/dblibs/WebDB.pm line 19.". It seems to find the module WebDB ok, but not the prepare subroutine in ::st
First here's my package (both packages are in one file, WebDB.pm)
package WebDB;
use strict;
use DBI;
sub connect {
my $dbh = (DBI->connect ("DBI:mysql:test:127.0.0.1", "root","",
{ PrintError => 1, RaiseError => 0 }));
return bless $dbh, 'WebDB::st';
}
package WebDB::st;
our #ISA = qw(::st);
sub prepare {
my ($self, $str, #args) = #_;
$self->SUPER::prepare("/* userid:$ENV{USER} */ $str", #args);
}
1;
I also tried replacing the "our #ISA = qw(;;st)" with "use base 'WebDB'" and same problem.
I'm thinking it's probably something very simple that I'm overlooking. Many thanks! Jane
Subclassing DBI has to be done just right to work correctly. Read Subclassing the DBI carefully and properly set RootClass (or explicitly call connect on your root class with #ISA set to DBI). Make sure you have WebDB::st subclassing DBI::st and a WebDB::db class subclassing DBI::db (even if there are no methods being overridden). No need to rebless.
Avoid using base; it has some unfortunate behavior that has led to its deprecation, particularly when used with classes that are not in a file of their own.
Either explicitly set #ISA or use the newer parent pragma:
package WebDB;
use parent 'DBI';
...
package WebDB::db;
use parent -norequire => 'DBI::db';
...
package WebDB::st;
use parent -norequire => 'DBI::st';
...
Are WebDB and WebDB::st in one file or two? If they are in separate files, I don't see anything that is doing a use WebDB::st;, which would cause that file to be loaded.
You can do either of these things as a remedy -- put the two packages in the same file (that would look exactly as you have pasted it above), or add a use WebDB::st; line in WebDB.pm.
(I'd also add use strict; use warnings; in both these packages too.)
Also, the prepare function is not in ::st -- there is no such package (unless it is defined elsewhere). prepare is in the WebDB::st namespace -- via the package declaration. You are however declaring that WebDB::st has ::st as a parent.
If subclassing is as tricky as ysth seems to think, I might recommend Class::Delegator from CPAN. I use if for classes that want to act like IO. And by it, Perl is the first language (that I am aware of) that has an expression language for aggregation, delegation, encapsulation almost equal with inheritance.
package WebDB;
use strict;
use DBI;
use Class::Delegator
send => [ qw<connect ...> ]
, to => '{_dbihandle}'
...
;
Lets say you have a parent Perl class in one file:
#!/usr/bin/perl
package Foo;
use strict;
use warnings;
use Data::Dumper;
sub new{
my $class = shift;
my %self = ();
return bless %self, $class;
}
1;
and a subclass in a different file:
#!/usr/bin/perl
package Bar;
use base "Foo";
1;
Will the subclass inherit the use statements from the parent? I know the method new will be inherited.
Basically I am trying to reduce the amount of boilerplate in my code and I can't find a clear answer to this question.
You asked in a comment about Test::Most and how it reduces boilerplate. Look at its import method. It's loading the modules into its namespace, adding those symbols to #EXPORT, then re-calling another import through a goto to finally get them into the calling namespace. It's some serious black magic that Curtis has going on there, although I wonder why he just didn't use something like import_to_level. Maybe there are some side effects I'm not thinking about.
I talk quite a bit about this sort of thing in Avoid accidently creating methods from module exports in The Effective Perler. It's in a different context but it's some of the same issues.
Here's a different example.
If some other module loads a module, you have access to it. It's not good to depend on that though. Here are three separate files:
Top.pm
use 5.010;
package Top;
use File::Spec;
sub announce { say "Hello from top!" }
1;
Bottom.pm
package Bottom;
use parent qw(Top);
sub catfiles { File::Spec->catfile( #_ ) }
1;
test.pl
use 5.010;
use Bottom;
say Bottom->catfiles( qw(foo bar baz) );
say File::Spec->catfile( qw( one two three ) );
I only load File::Spec in Top.pm. However, once loaded, I can use it anywhere in my Perl program. The output shows that I was able to "use" the module in other files even though I only loaded it in one:
Bottom/foo/bar/baz
one/two/three
For this to work, the part of the code that loads the module has to load before any other part of the code tries to use that module. As I said, it's a bad idea to depend on this: things break if the loading sequence changes or the loading module disappears.
If you want to import symbols, however, you have to explicitly load the module you want while you are in the package you want to import into. That's just so the exporting module defines the symbols in that package. It's not something that depends with scope.
Ah, good question!
Will the subclass inherit the use statements from the parent?
Well this depends on what you mean by inherit. I won't make any assumptions until the end, but the answer is maybe. You see, perl mixes the ideas of Classes, and Namespaces -- a package is a term that can describe either of them. Now the issue is the statement use all it does is force a package inclusion, and call the targets import() sub. This means it essentially has unlimited control over your package - and by way of that your class.
Now, compound this with all methods in perl being nothing more than subs that take $self as a first argument by convention and you're left with perl5. This has an enormous upside for those that know how to use it. While strict is a lexical pragma, what about Moose?
package BigMooseUser;
use Moose;
package BabyMooseUser;
our #ISA = 'BigMooseUser';
package Foo;
my $b = BabyMooseUser->new;
print $b->meta->name;
Now, where did BabyMooseUser get the constructor (new) from? Where did it get the meta class from? All of this is provided from a single use Moose; in the parent class (namespace). So
Will the subclass inherit the use statements from the parent?
Well, here, in our example, if the effects of the use statement are to add methods, than certainly.
This subject is kind of deep, and it depends if you're talking about pragmas, or more obscure object frameworks, or procedural modules. If you want to mitigate a parents namespace from affecting your own in the OO paradigm see namespace::autoclean.
For boilerplate reduction, I have a couple of strategies: Most of my classes are Moose classes, which takes care of OO setup and also gives me strict and warnings. If I want to have functions available in many packages, I'll create a project specific MyProject::Util module that uses Sub-Exporter to provide me with my own functions and my own interface. This makes it more consistent, and if I decide to change the Dumper (for example) later for whatever reason, I don't have to change lots of code. That'll also allow you to group exports. A class then usually looks something like this:
package Foo;
use Moose;
use MyProject::Util qw( :parsing :logging );
use namespace::autoclean;
# class implementation goes here
1;
If there's other things you regard as boilerplate and want to make simpler to include, it of course depends on what those things are.
A pragmatic answer to your problem: Either use, or look at how Modern::Perl does it to enforce strict and warnings.
You can get a definitive answer by examining the symbol tables for each package:
# examine-symbol-tables.pl
use Bar;
%parent_names = map{$_ => 1} keys %Foo::;
%child_names = map{$_ => 1} keys %Bar::;
delete $parent_names{$_} && ($common_names{$_} = delete $child_names{$_}) foreach keys %child_names;
print "Common names in symbol tables:\n";
print "#{[keys %common_names]}\n\n";
print "Unique names in Bar symbol table:\n";
print "#{[keys %child_names]}\n\n";
print "Unique names in Foo symbol table:\n";
print "#{[keys %parent_names]}\n\n";
$ perl inherit.pl
Common names in symbol tables:
BEGIN
Unique names in Bar symbol table:
ISA isa import
Unique names in Foo symbol table:
Dumper new VERSION