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PERLMROAPI(1)	       Perl Programmers	Reference Guide		 PERLMROAPI(1)

NAME
       perlmroapi - Perl method	resolution plugin interface

DESCRIPTION
       As of Perl 5.10.1 there is a new	interface for plugging and using
       method resolution orders	other than the default (linear depth first
       search).	 The C3	method resolution order	added in 5.10.0	has been re-
       implemented as a	plugin,	without	changing its Perl-space	interface.

       Each plugin should register itself by providing the following structure

	   struct mro_alg {
	       AV *(*resolve)(pTHX_ HV *stash, U32 level);
	       const char *name;
	       U16 length;
	       U16 kflags;
	       U32 hash;
	   };

       and calling "Perl_mro_register":

	   Perl_mro_register(aTHX_ &my_mro_alg);

       resolve
	   Pointer to the linearisation	function, described below.

       name
	   Name	of the MRO, either in ISO-8859-1 or UTF-8.

       length
	   Length of the name.

       kflags
	   If the name is given	in UTF-8, set this to "HVhek_UTF8". The	value
	   is passed direct as the parameter kflags to "hv_common()".

       hash
	   A precomputed hash value for	the MRO's name,	or 0.

Callbacks
       The "resolve" function is called	to generate a linearised ISA for the
       given stash, using this MRO. It is called with a	pointer	to the stash,
       and a level of 0. The core always sets level to 0 when it calls your
       function	- the parameter	is provided to allow your implementation to
       track depth if it needs to recurse.

       The function should return a reference to an array containing the
       parent classes in order.	The names of the classes should	be the result
       of calling "HvENAME()" on the stash. In those cases where "HvENAME()"
       returns null, "HvNAME()"	should be used instead.

       The caller is responsible for incrementing the reference	count of the
       array returned if it wants to keep the structure. Hence,	if you have
       created a temporary value that you keep no pointer to, "sv_2mortal()"
       to ensure that it is disposed of	correctly. If you have cached your
       return value, then return a pointer to it without changing the
       reference count.

Caching
       Computing MROs can be expensive.	The implementation provides a cache,
       in which	you can	store a	single "SV *", or anything that	can be cast to
       "SV *", such as "AV *". To read your private value, use the macro
       "MRO_GET_PRIVATE_DATA()", passing it the	"mro_meta" structure from the
       stash, and a pointer to your "mro_alg" structure:

	   meta	= HvMROMETA(stash);
	   private_sv =	MRO_GET_PRIVATE_DATA(meta, &my_mro_alg);

       To set your private value, call "Perl_mro_set_private_data()":

	   Perl_mro_set_private_data(aTHX_ meta, &c3_alg, private_sv);

       The private data	cache will take	ownership of a reference to
       private_sv, much	the same way that "hv_store()" takes ownership of a
       reference to the	value that you pass it.

Examples
       For examples of MRO implementations, see	"S_mro_get_linear_isa_c3()"
       and the "BOOT:" section of ext/mro/mro.xs, and
       "S_mro_get_linear_isa_dfs()" in mro_core.c

AUTHORS
       The implementation of the C3 MRO	and switchable MROs within the perl
       core was	written	by Brandon L Black. Nicholas Clark created the
       pluggable interface, refactored Brandon's implementation	to work	with
       it, and wrote this document.

perl v5.26.0			  2017-04-19			 PERLMROAPI(1)

NAME | DESCRIPTION | Callbacks | Caching | Examples | AUTHORS

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