NAME

Module::Runtime - runtime module handling

SYNOPSIS

        use Module::Runtime qw(is_valid_module_name require_module
                        use_module use_package_optimistically
                        is_valid_module_spec compose_module_name);

        $ok = is_valid_module_name($module);
        require_module($module);

        $bi = use_module("Math::BigInt", 1.31)->new("1_234");
        $widget = use_package_optimistically("Local::Widget")->new;

        $ok = is_valid_module_spec("Standard::Prefix", $spec);
        $module_name = compose_module_name("Standard::Prefix",
                                                $spec);

DESCRIPTION

The functions exported by this module deal with runtime handling of Perl modules, which are normally handled at compile time.

FUNCTIONS

is_valid_module_name(STRING)

This tests whether a string is a valid Perl module name, i.e., has valid bareword syntax. The rule for this, precisely, is: the string must consist of one or more segments separated by ::; each segment must consist of one or more identifier characters (alphanumerics plus "_"); the first character of the string must not be a digit. Thus IO::File, warnings, and foo::123::x_0 are all valid module names, whereas IO:: and 1foo::bar are not.

Note that ' separators are not permitted by this function.

require_module(NAME)

This is essentially the bareword form of require, in runtime form. The NAME is a string, which should be a valid module name (one or more ::-separated segments). If it is not a valid name, the function dies.

The module specified by NAME is loaded, if it hasn't been already, in the manner of the bareword form of require. That means that a search through @INC is performed, and a byte-compiled form of the module will be used if available.

The return value is as for require. That is, it is the value returned by the module itself if the module is loaded anew, or 1 if the module was already loaded.

use_module(NAME[, VERSION])

This is essentially use in runtime form, but without the "import" feature (which is fundamentally a compile-time thing). The NAME is handled just like in require_module above: it must be a module name, and the named module is loaded as if by the bareword form of require.

If a VERSION is specified, the "VERSION" method of the loaded module is called with the specified VERSION as an argument. This normally serves to ensure that the version loaded is at least the version required. This is the same functionality provided by the VERSION parameter of use.

On success, the name of the module is returned. This is unlike require_module, and is done so that the entire call to use_module can be used as a class name to call a constructor, as in the example in the synopsis.

use_package_optimistically(NAME[, VERSION])

This is an analogue of use_module for the situation where there is uncertainty as to whether a package/class is defined in its own module or by some other means. It attempts to arrange for the named package to be available, either by loading a module or by doing nothing and hoping.

If the package does not appear to already be loaded then an attempt is made to load the module of the same name (as if by the bareword form of require). If the module cannot be found then it is assumed that the package was actually already loaded but wasn't detected correctly, and no error is signalled. That's the optimistic bit.

For the purposes of this function, package existence is checked by whether a $VERSION variable exists in the package. If the module wasn't found, or if it was loaded but didn't create a $VERSION variable, then such a variable is automatically created (with value undef) so that repeated use of this function won't redundantly attempt to load the module.

This is mostly the same operation that is performed by the base pragma to ensure that the specified base classes are available. The difference is that base does not allow the $VERSION variable to remain undefined: it will set it to "-1, set by base.pm" if it does not otherwise have a non-null value.

If a VERSION is specified, the "VERSION" method of the loaded package is called with the specified VERSION as an argument. This normally serves to ensure that the version loaded is at least the version required. On success, the name of the package is returned. These aspects of the function work just like use_module.

is_valid_module_spec(PREFIX, SPEC)

Tests whether SPEC is valid input for compose_module_name(). See below for what that entails. Whether a PREFIX is supplied affects the validity of SPEC, but the exact value of the prefix is unimportant, so this function treats PREFIX as a boolean.

compose_module_name(PREFIX, SPEC)

This function is intended to make it more convenient for a user to specify a Perl module name at runtime. Users have greater need for abbreviations and context-sensitivity than programmers, and Perl module names get a little unwieldy. SPEC is what the user specifies, and this function translates it into a module name in standard form, which it returns.

SPEC has syntax approximately that of a standard module name: it should consist of one or more name segments, each of which consists of one or more identifier characters. However, / is permitted as a separator, in addition to the standard ::. The two separators are entirely interchangeable.

Additionally, if PREFIX is not undef then it must be a module name in standard form, and it is prefixed to the user-specified name. The user can inhibit the prefix addition by starting SPEC with a separator (either / or ::).

SEE ALSO

base, "require" in perlfunc, "use" in perlfunc

AUTHOR

Andrew Main (Zefram) <zefram@fysh.org>

COPYRIGHT

Copyright (C) 2004, 2006, 2007 Andrew Main (Zefram) <zefram@fysh.org>

LICENSE

This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.