perlmroapi

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 v5.30.0                      2023-11-23                     PERLMROAPI(1)