How to import names from a dynamically required module

jds17 has asked for the wisdom of the Perl Monks concerning the following question:

Hi,
I have written a module where I would like to use Role::Basic. At runtime, I want to require a specific module consuming such a role and also to import some of its names.
I could not get the import of the names right. What I tried is the following:

my $package_name = get_package_name();

eval "require $package_name";
eval "$package_name->import(
        qw( method1 method2 method3 )";
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Here, $package_name is the fully qualified name of the role consuming package determined at runtime and method1,... are methods exported by this package.
What I get as an error is:

Undefined subroutine &MyPackage::num_records called at ...
[download]

where MyPackage is the name of the current package (i.e. the one the above code is in) and not the desired one, i.e. $package_name.

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Re: How to import names from a dynamically required module by tobyink (Canon) on Oct 02, 2012 at 22:06 UTC
`if (eval "require $package_name; 1") { $package_name->import(qw/method1 method2 method3/); }` [download] It's often a good idea to lift imports to compile-time using a `BEGIN` block. `perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'`	[reply] [d/l] [select]
Re^2: How to import names from a dynamically required module by jds17 (Pilgrim) on Oct 02, 2012 at 22:20 UTC
Thank you very much, tobyink, I was not aware of the fact that one could call import on package names as in your example. This solved my issue.	[reply]
Re^3: How to import names from a dynamically required module by tobyink (Canon) on Oct 03, 2012 at 06:35 UTC
This is not specific to `import`; it works with all class method calls... `use Math::BigInt; my $class = "Math::BigInt"; my $six = $class->new(6); my $seven = "Math::BigInt"->new(7); my $eight = join("::", "Math", "BigInt")->new(8);` [download] In fact, string quoting class names is arguably a much better idea than the more conventional `Math::BigInt->new(9)`, because the latter will start behaving surprisingly if there's ever a `BigInt` sub defined in the `Math` package. `perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'`	[reply] [d/l] [select]
Re^4: How to import names from a dynamically required module by choroba (Cardinal) on Oct 03, 2012 at 08:05 UTC
Re^5: How to import names from a dynamically required module by tobyink (Canon) on Oct 03, 2012 at 08:59 UTC
Re^5: How to import names from a dynamically required module by Anonymous Monk on Oct 03, 2012 at 08:55 UTC
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Re: How to import names from a dynamically required module by chromatic (Archbishop) on Oct 02, 2012 at 23:02 UTC
Use something Class::Load rather than eval STRING; almost no one checks `$package_name` for sanity. If that comes from anything at all untrusted, you have a code injection vulnerability. Improve your skills with Modern Perl: the free book.	[reply] [d/l]
Re^2: How to import names from a dynamically required module by jds17 (Pilgrim) on Oct 02, 2012 at 23:13 UTC
chromatic, you are right. I will strip out eval completely and use Class::Load.	[reply]
Re: How to import names from a dynamically required module by kejohm (Hermit) on Oct 02, 2012 at 22:21 UTC
There is a syntax error in your second eval; you are missing a `)`, so the code isn't being executed. After `eval`ing code you should either check the value of the `$@` variable, or check the return value from `eval`, like tobyink's example above.	[reply] [d/l] [select]
Re^2: How to import names from a dynamically required module by jds17 (Pilgrim) on Oct 02, 2012 at 23:06 UTC
Thanks, kejohm. You are right, that was a stupid error on my side. I like the version without the eval as in tobyink's example better in any case.	[reply]