


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 with
       "Perl_mro_register" by providing the following structure

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

       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 caller is
       responsible for incrementing the reference count 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



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


       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
       mro/mro.xs, and "S_mro_get_linear_isa_dfs()" in mro.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.























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