1PERLMROAPI(1) Perl Programmers Reference Guide PERLMROAPI(1)
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6 perlmroapi - Perl method resolution plugin interface
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9 As of Perl 5.10.1 there is a new interface for plugging and using
10 method resolution orders other than the default (linear depth first
11 search). The C3 method resolution order added in 5.10.0 has been re-
12 implemented as a plugin, without changing its Perl-space interface.
13 Each plugin should register itself by providing the following structure
15 struct mro_alg {
17 AV *(*resolve)(pTHX_ HV *stash, U32 level);
18 const char *name;
19 U16 length;
20 U16 kflags;
21 U32 hash;
22 };
23 and calling "Perl_mro_register":
25 Perl_mro_register(aTHX_ &my_mro_alg);
27 resolve
29 Pointer to the linearisation function, described below.
30 name
32 Name of the MRO, either in ISO-8859-1 or UTF-8.
33 length
35 Length of the name.
36 kflags
38 If the name is given in UTF-8, set this to "HVhek_UTF8". The value
39 is passed direct as the parameter kflags to "hv_common()".
40 hash
42 A precomputed hash value for the MRO's name, or 0.
43
45 The "resolve" function is called to generate a linearised ISA for the
46 given stash, using this MRO. It is called with a pointer to the stash,
47 and a level of 0. The core always sets level to 0 when it calls your
48 function - the parameter is provided to allow your implementation to
49 track depth if it needs to recurse.
50 The function should return a reference to an array containing the
52 parent classes in order. The names of the classes should be the result
53 of calling "HvENAME()" on the stash. In those cases where "HvENAME()"
54 returns null, "HvNAME()" should be used instead.
55 The caller is responsible for incrementing the reference count of the
57 array returned if it wants to keep the structure. Hence, if you have
58 created a temporary value that you keep no pointer to, "sv_2mortal()"
59 to ensure that it is disposed of correctly. If you have cached your
60 return value, then return a pointer to it without changing the
61 reference count.
62
64 Computing MROs can be expensive. The implementation provides a cache,
65 in which you can store a single "SV *", or anything that can be cast to
66 "SV *", such as "AV *". To read your private value, use the macro
67 "MRO_GET_PRIVATE_DATA()", passing it the "mro_meta" structure from the
68 stash, and a pointer to your "mro_alg" structure:
69 meta = HvMROMETA(stash);
71 private_sv = MRO_GET_PRIVATE_DATA(meta, &my_mro_alg);
72 To set your private value, call "Perl_mro_set_private_data()":
74 Perl_mro_set_private_data(aTHX_ meta, &c3_alg, private_sv);
76 The private data cache will take ownership of a reference to
78 private_sv, much the same way that "hv_store()" takes ownership of a
79 reference to the value that you pass it.
80
82 For examples of MRO implementations, see "S_mro_get_linear_isa_c3()"
83 and the "BOOT:" section of ext/mro/mro.xs, and
84 "S_mro_get_linear_isa_dfs()" in mro_core.c
85
87 The implementation of the C3 MRO and switchable MROs within the perl
88 core was written by Brandon L Black. Nicholas Clark created the
89 pluggable interface, refactored Brandon's implementation to work with
90 it, and wrote this document.
91perl v5.34.0 2021-10-18 PERLMROAPI(1)