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
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
|
.\" -*- 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 "Tie::Hash 3pm"
.TH Tie::Hash 3pm 2023-11-28 "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
Tie::Hash, Tie::StdHash, Tie::ExtraHash \- base class definitions for tied hashes
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 2
\& package NewHash;
\& require Tie::Hash;
\&
\& @ISA = qw(Tie::Hash);
\&
\& sub DELETE { ... } # Provides needed method
\& sub CLEAR { ... } # Overrides inherited method
\&
\&
\& package NewStdHash;
\& require Tie::Hash;
\&
\& @ISA = qw(Tie::StdHash);
\&
\& # All methods provided by default, define
\& # only those needing overrides
\& # Accessors access the storage in %{$_[0]};
\& # TIEHASH should return a reference to the actual storage
\& sub DELETE { ... }
\&
\& package NewExtraHash;
\& require Tie::Hash;
\&
\& @ISA = qw(Tie::ExtraHash);
\&
\& # All methods provided by default, define
\& # only those needing overrides
\& # Accessors access the storage in %{$_[0][0]};
\& # TIEHASH should return an array reference with the first element
\& # being the reference to the actual storage
\& sub DELETE {
\& $_[0][1]\->(\*(Aqdel\*(Aq, $_[0][0], $_[1]); # Call the report writer
\& delete $_[0][0]\->{$_[1]}; # $_[0]\->SUPER::DELETE($_[1])
\& }
\&
\&
\& package main;
\&
\& tie %new_hash, \*(AqNewHash\*(Aq;
\& tie %new_std_hash, \*(AqNewStdHash\*(Aq;
\& tie %new_extra_hash, \*(AqNewExtraHash\*(Aq,
\& sub {warn "Doing \eU$_[1]\eE of $_[2].\en"};
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
This module provides some skeletal methods for hash-tying classes. See
perltie for a list of the functions required in order to tie a hash
to a package. The basic \fBTie::Hash\fR package provides a \f(CW\*(C`new\*(C'\fR method, as well
as methods \f(CW\*(C`TIEHASH\*(C'\fR, \f(CW\*(C`EXISTS\*(C'\fR and \f(CW\*(C`CLEAR\*(C'\fR. The \fBTie::StdHash\fR and
\&\fBTie::ExtraHash\fR packages
provide most methods for hashes described in perltie (the exceptions
are \f(CW\*(C`UNTIE\*(C'\fR and \f(CW\*(C`DESTROY\*(C'\fR). They cause tied hashes to behave exactly like standard hashes,
and allow for selective overwriting of methods. \fBTie::Hash\fR has legacy support for the
\&\f(CW\*(C`new\*(C'\fR method: it is used if \f(CW\*(C`TIEHASH\*(C'\fR is not defined
in the case a class forgets to include a \f(CW\*(C`TIEHASH\*(C'\fR method.
.PP
For developers wishing to write their own tied hashes, the required methods
are briefly defined below. See the perltie section for more detailed
descriptive, as well as example code:
.IP "TIEHASH classname, LIST" 4
.IX Item "TIEHASH classname, LIST"
The method invoked by the command \f(CW\*(C`tie %hash, classname\*(C'\fR. Associates a new
hash instance with the specified class. \f(CW\*(C`LIST\*(C'\fR would represent additional
arguments (along the lines of AnyDBM_File and compatriots) needed to
complete the association.
.IP "STORE this, key, value" 4
.IX Item "STORE this, key, value"
Store datum \fIvalue\fR into \fIkey\fR for the tied hash \fIthis\fR.
.IP "FETCH this, key" 4
.IX Item "FETCH this, key"
Retrieve the datum in \fIkey\fR for the tied hash \fIthis\fR.
.IP "FIRSTKEY this" 4
.IX Item "FIRSTKEY this"
Return the first key in the hash.
.IP "NEXTKEY this, lastkey" 4
.IX Item "NEXTKEY this, lastkey"
Return the next key in the hash.
.IP "EXISTS this, key" 4
.IX Item "EXISTS this, key"
Verify that \fIkey\fR exists with the tied hash \fIthis\fR.
.Sp
The \fBTie::Hash\fR implementation is a stub that simply croaks.
.IP "DELETE this, key" 4
.IX Item "DELETE this, key"
Delete the key \fIkey\fR from the tied hash \fIthis\fR.
.IP "CLEAR this" 4
.IX Item "CLEAR this"
Clear all values from the tied hash \fIthis\fR.
.IP "SCALAR this" 4
.IX Item "SCALAR this"
Returns what evaluating the hash in scalar context yields.
.Sp
\&\fBTie::Hash\fR does not implement this method (but \fBTie::StdHash\fR
and \fBTie::ExtraHash\fR do).
.SH "Inheriting from \fBTie::StdHash\fP"
.IX Header "Inheriting from Tie::StdHash"
The accessor methods assume that the actual storage for the data in the tied
hash is in the hash referenced by \f(CWtied(%tiedhash)\fR. Thus overwritten
\&\f(CW\*(C`TIEHASH\*(C'\fR method should return a hash reference, and the remaining methods
should operate on the hash referenced by the first argument:
.PP
.Vb 2
\& package ReportHash;
\& our @ISA = \*(AqTie::StdHash\*(Aq;
\&
\& sub TIEHASH {
\& my $storage = bless {}, shift;
\& warn "New ReportHash created, stored in $storage.\en";
\& $storage
\& }
\& sub STORE {
\& warn "Storing data with key $_[1] at $_[0].\en";
\& $_[0]{$_[1]} = $_[2]
\& }
.Ve
.SH "Inheriting from \fBTie::ExtraHash\fP"
.IX Header "Inheriting from Tie::ExtraHash"
The accessor methods assume that the actual storage for the data in the tied
hash is in the hash referenced by \f(CW\*(C`(tied(%tiedhash))\->[0]\*(C'\fR. Thus overwritten
\&\f(CW\*(C`TIEHASH\*(C'\fR method should return an array reference with the first
element being a hash reference, and the remaining methods should operate on the
hash \f(CW\*(C`%{ $_[0]\->[0] }\*(C'\fR:
.PP
.Vb 2
\& package ReportHash;
\& our @ISA = \*(AqTie::ExtraHash\*(Aq;
\&
\& sub TIEHASH {
\& my $class = shift;
\& my $storage = bless [{}, @_], $class;
\& warn "New ReportHash created, stored in $storage.\en";
\& $storage;
\& }
\& sub STORE {
\& warn "Storing data with key $_[1] at $_[0].\en";
\& $_[0][0]{$_[1]} = $_[2]
\& }
.Ve
.PP
The default \f(CW\*(C`TIEHASH\*(C'\fR method stores "extra" arguments to \fBtie()\fR starting
from offset 1 in the array referenced by \f(CWtied(%tiedhash)\fR; this is the
same storage algorithm as in TIEHASH subroutine above. Hence, a typical
package inheriting from \fBTie::ExtraHash\fR does not need to overwrite this
method.
.ie n .SH """SCALAR"", ""UNTIE"" and ""DESTROY"""
.el .SH "\f(CWSCALAR\fP, \f(CWUNTIE\fP and \f(CWDESTROY\fP"
.IX Header "SCALAR, UNTIE and DESTROY"
The methods \f(CW\*(C`UNTIE\*(C'\fR and \f(CW\*(C`DESTROY\*(C'\fR are not defined in \fBTie::Hash\fR,
\&\fBTie::StdHash\fR, or \fBTie::ExtraHash\fR. Tied hashes do not require
presence of these methods, but if defined, the methods will be called in
proper time, see perltie.
.PP
\&\f(CW\*(C`SCALAR\*(C'\fR is only defined in \fBTie::StdHash\fR and \fBTie::ExtraHash\fR.
.PP
If needed, these methods should be defined by the package inheriting from
\&\fBTie::Hash\fR, \fBTie::StdHash\fR, or \fBTie::ExtraHash\fR. See "SCALAR" in perltie
to find out what happens when \f(CW\*(C`SCALAR\*(C'\fR does not exist.
.SH "MORE INFORMATION"
.IX Header "MORE INFORMATION"
The packages relating to various DBM-related implementations (\fIDB_File\fR,
\&\fINDBM_File\fR, etc.) show examples of general tied hashes, as does the
Config module. While these do not utilize \fBTie::Hash\fR, they serve as
good working examples.
|
