note strict/lax version requirements in documentation
[p5sagit/p5-mst-13.2.git] / pod / perlmroapi.pod
CommitLineData
15932acc 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