Edit File: perlmroapi.pod
=head1 NAME perlmroapi - Perl method resolution plugin interface =head1 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 C<Perl_mro_register>: Perl_mro_register(aTHX_ &my_mro_alg); =over 4 =item resolve Pointer to the linearisation function, described below. =item name Name of the MRO, either in ISO-8859-1 or UTF-8. =item length Length of the name. =item kflags If the name is given in UTF-8, set this to C<HVhek_UTF8>. The value is passed direct as the parameter I<kflags> to C<hv_common()>. =item hash A precomputed hash value for the MRO's name, or 0. =back =head1 Callbacks The C<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 I<level> of 0. The core always sets I<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 C<HvENAME()> on the stash. In those cases where C<HvENAME()> returns null, C<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, C<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. =head1 Caching Computing MROs can be expensive. The implementation provides a cache, in which you can store a single C<SV *>, or anything that can be cast to C<SV *>, such as C<AV *>. To read your private value, use the macro C<MRO_GET_PRIVATE_DATA()>, passing it the C<mro_meta> structure from the stash, and a pointer to your C<mro_alg> structure: meta = HvMROMETA(stash); private_sv = MRO_GET_PRIVATE_DATA(meta, &my_mro_alg); To set your private value, call C<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 C<hv_store()> takes ownership of a reference to the value that you pass it. =head1 Examples For examples of MRO implementations, see C<S_mro_get_linear_isa_c3()> and the C<BOOT:> section of F<ext/mro/mro.xs>, and C<S_mro_get_linear_isa_dfs()> in F<mro_core.c> =head1 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. =cut
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