.\" Automatically generated by Pod::Man 4.14 (Pod::Simple 3.40) .\" .\" 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 .. .\" Set up some character translations and predefined strings. \*(-- will .\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left .\" double quote, and \*(R" will give a right double quote. \*(C+ will .\" give a nicer C++. Capital omega is used to do unbreakable dashes and .\" therefore won't be available. \*(C` and \*(C' expand to `' in nroff, .\" nothing in troff, for use with C<>. .tr \(*W- .ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p' .ie n \{\ . ds -- \(*W- . ds PI pi . if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch . if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\" diablo 12 pitch . ds L" "" . ds R" "" . ds C` "" . ds C' "" 'br\} .el\{\ . ds -- \|\(em\| . ds PI \(*p . ds L" `` . ds R" '' . 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::Memoize 3perl" .TH Tie::Memoize 3perl "2021-09-24" "perl v5.32.1" "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::Memoize \- add data to hash when needed .SH "SYNOPSIS" .IX Header "SYNOPSIS" .Vb 5 \& require Tie::Memoize; \& tie %hash, \*(AqTie::Memoize\*(Aq, \& \e&fetch, # The rest is optional \& $DATA, \e&exists, \& {%ini_value}, {%ini_existence}; .Ve .SH "DESCRIPTION" .IX Header "DESCRIPTION" This package allows a tied hash to autoload its values on the first access, and to use the cached value on the following accesses. .PP Only read-accesses (via fetching the value or \f(CW\*(C`exists\*(C'\fR) result in calls to the functions; the modify-accesses are performed as on a normal hash. .PP The required arguments during \f(CW\*(C`tie\*(C'\fR are the hash, the package, and the reference to the \f(CW\*(C`FETCH\*(C'\fRing function. The optional arguments are an arbitrary scalar \f(CW$data\fR, the reference to the \f(CW\*(C`EXISTS\*(C'\fR function, and initial values of the hash and of the existence cache. .PP Both the \f(CW\*(C`FETCH\*(C'\fRing function and the \f(CW\*(C`EXISTS\*(C'\fR functions have the same signature: the arguments are \f(CW\*(C`$key, $data\*(C'\fR; \f(CW$data\fR is the same value as given as argument during \fBtie()\fRing. Both functions should return an empty list if the value does not exist. If \f(CW\*(C`EXISTS\*(C'\fR function is different from the \f(CW\*(C`FETCH\*(C'\fRing function, it should return a \s-1TRUE\s0 value on success. The \f(CW\*(C`FETCH\*(C'\fRing function should return the intended value if the key is valid. .SH "Inheriting from \fBTie::Memoize\fP" .IX Header "Inheriting from Tie::Memoize" The structure of the \fBtied()\fR data is an array reference with elements .PP .Vb 5 \& 0: cache of known values \& 1: cache of known existence of keys \& 2: FETCH function \& 3: EXISTS function \& 4: $data .Ve .PP The rest is for internal usage of this package. In particular, if \&\s-1TIEHASH\s0 is overwritten, it should call \s-1SUPER::TIEHASH.\s0 .SH "EXAMPLE" .IX Header "EXAMPLE" .Vb 6 \& sub slurp { \& my ($key, $dir) = shift; \& open my $h, \*(Aq<\*(Aq, "$dir/$key" or return; \& local $/; <$h> # slurp it all \& } \& sub exists { my ($key, $dir) = shift; return \-f "$dir/$key" } \& \& tie %hash, \*(AqTie::Memoize\*(Aq, \e&slurp, $directory, \e&exists, \& { fake_file1 => $content1, fake_file2 => $content2 }, \& { pretend_does_not_exists => 0, known_to_exist => 1 }; .Ve .PP This example treats the slightly modified contents of \f(CW$directory\fR as a hash. The modifications are that the keys \fIfake_file1\fR and \&\fIfake_file2\fR fetch values \f(CW$content1\fR and \f(CW$content2\fR, and \&\fIpretend_does_not_exists\fR will never be accessed. Additionally, the existence of \fIknown_to_exist\fR is never checked (so if it does not exists when its content is needed, the user of \f(CW%hash\fR may be confused). .SH "BUGS" .IX Header "BUGS" \&\s-1FIRSTKEY\s0 and \s-1NEXTKEY\s0 methods go through the keys which were already read, not all the possible keys of the hash. .SH "AUTHOR" .IX Header "AUTHOR" Ilya Zakharevich .