1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
|
.\" -*- mode: troff; coding: utf-8 -*-
.\" Automatically generated by Pod::Man 5.01 (Pod::Simple 3.43)
.\"
.\" Standard preamble:
.\" ========================================================================
.de Sp \" Vertical space (when we can't use .PP)
.if t .sp .5v
.if n .sp
..
.de Vb \" Begin verbatim text
.ft CW
.nf
.ne \\$1
..
.de Ve \" End verbatim text
.ft R
.fi
..
.\" \*(C` and \*(C' are quotes in nroff, nothing in troff, for use with C<>.
.ie n \{\
. ds C` ""
. ds C' ""
'br\}
.el\{\
. ds C`
. ds C'
'br\}
.\"
.\" Escape single quotes in literal strings from groff's Unicode transform.
.ie \n(.g .ds Aq \(aq
.el .ds Aq '
.\"
.\" If the F register is >0, we'll generate index entries on stderr for
.\" titles (.TH), headers (.SH), subsections (.SS), items (.Ip), and index
.\" entries marked with X<> in POD. Of course, you'll have to process the
.\" output yourself in some meaningful fashion.
.\"
.\" Avoid warning from groff about undefined register 'F'.
.de IX
..
.nr rF 0
.if \n(.g .if rF .nr rF 1
.if (\n(rF:(\n(.g==0)) \{\
. if \nF \{\
. de IX
. tm Index:\\$1\t\\n%\t"\\$2"
..
. if !\nF==2 \{\
. nr % 0
. nr F 2
. \}
. \}
.\}
.rr rF
.\" ========================================================================
.\"
.IX Title "PERLMROAPI 1"
.TH PERLMROAPI 1 2024-05-30 "perl v5.38.2" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification. Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH NAME
perlmroapi \- Perl method resolution plugin interface
.SH DESCRIPTION
.IX Header "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.
.PP
Each plugin should register itself by providing
the following structure
.PP
.Vb 7
\& struct mro_alg {
\& AV *(*resolve)(pTHX_ HV *stash, U32 level);
\& const char *name;
\& U16 length;
\& U16 kflags;
\& U32 hash;
\& };
.Ve
.PP
and calling \f(CW\*(C`Perl_mro_register\*(C'\fR:
.PP
.Vb 1
\& Perl_mro_register(aTHX_ &my_mro_alg);
.Ve
.IP resolve 4
.IX Item "resolve"
Pointer to the linearisation function, described below.
.IP name 4
.IX Item "name"
Name of the MRO, either in ISO\-8859\-1 or UTF\-8.
.IP length 4
.IX Item "length"
Length of the name.
.IP kflags 4
.IX Item "kflags"
If the name is given in UTF\-8, set this to \f(CW\*(C`HVhek_UTF8\*(C'\fR. The value is passed
direct as the parameter \fIkflags\fR to \f(CWhv_common()\fR.
.IP hash 4
.IX Item "hash"
A precomputed hash value for the MRO's name, or 0.
.SH Callbacks
.IX Header "Callbacks"
The \f(CW\*(C`resolve\*(C'\fR 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 \fIlevel\fR of 0. The core always sets \fIlevel\fR to 0 when it calls your
function \- the parameter is provided to allow your implementation to track
depth if it needs to recurse.
.PP
The function should return a reference to an array containing string SVs
giving the names of parent classes in order. The names of the classes should
be the result of calling \f(CWHvENAME()\fR on the stash. In those cases where
\&\f(CWHvENAME()\fR returns null, \f(CWHvNAME()\fR should be used instead.
.PP
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, \f(CWsv_2mortal()\fR 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.
.SH Caching
.IX Header "Caching"
Computing MROs can be expensive. The implementation provides a cache, in
which you can store a single \f(CW\*(C`SV *\*(C'\fR, or anything that can be cast to
\&\f(CW\*(C`SV *\*(C'\fR, such as \f(CW\*(C`AV *\*(C'\fR. To read your private value, use the macro
\&\f(CWMRO_GET_PRIVATE_DATA()\fR, passing it the \f(CW\*(C`mro_meta\*(C'\fR structure from the
stash, and a pointer to your \f(CW\*(C`mro_alg\*(C'\fR structure:
.PP
.Vb 2
\& meta = HvMROMETA(stash);
\& private_sv = MRO_GET_PRIVATE_DATA(meta, &my_mro_alg);
.Ve
.PP
To set your private value, call \f(CWPerl_mro_set_private_data()\fR:
.PP
.Vb 1
\& Perl_mro_set_private_data(aTHX_ meta, &c3_alg, private_sv);
.Ve
.PP
The private data cache will take ownership of a reference to private_sv,
much the same way that \f(CWhv_store()\fR takes ownership of a reference to the
value that you pass it.
.SH Examples
.IX Header "Examples"
For examples of MRO implementations, see \f(CWS_mro_get_linear_isa_c3()\fR
and the \f(CW\*(C`BOOT:\*(C'\fR section of \fIext/mro/mro.xs\fR, and
\&\f(CWS_mro_get_linear_isa_dfs()\fR in \fImro_core.c\fR
.SH AUTHORS
.IX Header "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.
|
