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

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

NNAAMMEE #

 perlmroapi - Perl method resolution plugin interface

DDEESSCCRRIIPPTTIIOONN #

 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 _k_f_l_a_g_s to "hv_common()".

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

CCaallllbbaacckkss 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 _l_e_v_e_l of 0. The core always sets _l_e_v_e_l 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.

CCaacchhiinngg 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.

EExxaammpplleess For examples of MRO implementations, see “S_mro_get_linear_isa_c3()” and the “BOOT:” section of _e_x_t_/_m_r_o_/_m_r_o_._x_s, and “S_mro_get_linear_isa_dfs()” in _m_r_o___c_o_r_e_._c

AAUUTTHHOORRSS #

 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 v5.36.3 2023-02-15 PERLMROAPI(1)