1=head1 NAME 2 3perlmroapi - Perl method resolution plugin interface 4 5=head1 DESCRIPTION 6 7As of Perl 5.10.1 there is a new interface for plugging and using method 8resolution orders other than the default (linear depth first search). 9The C3 method resolution order added in 5.10.0 has been re-implemented as 10a plugin, without changing its Perl-space interface. 11 12Each plugin should register itself with C<Perl_mro_register> by providing 13the following structure 14 15 struct mro_alg { 16 AV *(*resolve)(pTHX_ HV *stash, U32 level); 17 const char *name; 18 U16 length; 19 U16 kflags; 20 U32 hash; 21 }; 22 23=over 4 24 25=item resolve 26 27Pointer to the linearisation function, described below. 28 29=item name 30 31Name of the MRO, either in ISO-8859-1 or UTF-8. 32 33=item length 34 35Length of the name. 36 37=item kflags 38 39If the name is given in UTF-8, set this to C<HVhek_UTF8>. The value is passed 40direct as the parameter I<kflags> to C<hv_common()>. 41 42=item hash 43 44A precomputed hash value for the MRO's name, or 0. 45 46=back 47 48=head1 Callbacks 49 50The C<resolve> function is called to generate a linearised ISA for the 51given stash, using this MRO. It is called with a pointer to the stash, and 52a I<level> of 0. The core always sets I<level> to 0 when it calls your 53function - the parameter is provided to allow your implementation to track 54depth if it needs to recurse. 55 56The function should return a reference to an array containing the parent 57classes in order. The caller is responsible for incrementing the reference 58count if it wants to keep the structure. Hence if you have created a 59temporary value that you keep no pointer to, C<sv_2mortal()> to ensure that 60it is disposed of correctly. If you have cached your return value, then 61return a pointer to it without changing the reference count. 62 63=head1 Caching 64 65Computing MROs can be expensive. The implementation provides a cache, in 66which you can store a single C<SV *>, or anything that can be cast to 67C<SV *>, such as C<AV *>. To read your private value, use the macro 68C<MRO_GET_PRIVATE_DATA()>, passing it the C<mro_meta> structure from the 69stash, and a pointer to your C<mro_alg> structure: 70 71 meta = HvMROMETA(stash); 72 private_sv = MRO_GET_PRIVATE_DATA(meta, &my_mro_alg); 73 74To set your private value, call C<Perl_mro_set_private_data()>: 75 76 Perl_mro_set_private_data(aTHX_ meta, &c3_alg, private_sv); 77 78The private data cache will take ownership of a reference to private_sv, 79much the same way that C<hv_store()> takes ownership of a reference to the 80value that you pass it. 81 82=head1 Examples 83 84For examples of MRO implementations, see C<S_mro_get_linear_isa_c3()> 85and the C<BOOT:> section of F<mro/mro.xs>, and C<S_mro_get_linear_isa_dfs()> 86in F<mro.c> 87 88=head1 AUTHORS 89 90The implementation of the C3 MRO and switchable MROs within the perl core was 91written by Brandon L Black. Nicholas Clark created the pluggable interface, 92refactored Brandon's implementation to work with it, and wrote this document. 93 94=cut 95