1Eval::Closure(3) User Contributed Perl Documentation Eval::Closure(3)
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6 Eval::Closure - safely and cleanly create closures via string eval
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9 version 0.14
10
12 use Eval::Closure;
13 my $code = eval_closure(
15 source => 'sub { $foo++ }',
16 environment => {
17 '$foo' => \1,
18 },
19 );
20 warn $code->(); # 1
22 warn $code->(); # 2
23 my $code2 = eval_closure(
25 source => 'sub { $code->() }',
26 ); # dies, $code isn't in scope
27
29 String eval is often used for dynamic code generation. For instance,
30 "Moose" uses it heavily, to generate inlined versions of accessors and
31 constructors, which speeds code up at runtime by a significant amount.
32 String eval is not without its issues however - it's difficult to
33 control the scope it's used in (which determines which variables are in
34 scope inside the eval), and it's easy to miss compilation errors, since
35 eval catches them and sticks them in $@ instead.
36 This module attempts to solve these problems. It provides an
38 "eval_closure" function, which evals a string in a clean environment,
39 other than a fixed list of specified variables. Compilation errors are
40 rethrown automatically.
41
43 eval_closure(%args)
44 This function provides the main functionality of this module. It is
45 exported by default. It takes a hash of parameters, with these keys
46 being valid:
47 source
49 The string to be evaled. It should end by returning a code
50 reference. It can access any variable declared in the "environment"
51 parameter (and only those variables). It can be either a string, or
52 an arrayref of lines (which will be joined with newlines to produce
53 the string).
54 environment
56 The environment to provide to the eval. This should be a hashref,
57 mapping variable names (including sigils) to references of the
58 appropriate type. For instance, a valid value for environment would
59 be "{ '@foo' => [] }" (which would allow the generated function to
60 use an array named @foo). Generally, this is used to allow the
61 generated function to access externally defined variables (so you
62 would pass in a reference to a variable that already exists).
63 In perl 5.18 and greater, the environment hash can contain
65 variables with a sigil of "&". This will create a lexical sub in
66 the evaluated code (see "The 'lexical_subs' feature" in feature).
67 Using a "&" sigil on perl versions before lexical subs were
68 available will throw an error.
69 alias
71 If set to true, the coderef returned closes over the variables
72 referenced in the environment hashref. (This feature requires
73 Devel::LexAlias.) If set to false, the coderef closes over a
74 shallow copy of the variables.
75 If this argument is omitted, Eval::Closure will currently assume
77 false, but this assumption may change in a future version.
78 description
80 This lets you provide a bit more information in backtraces.
81 Normally, when a function that was generated through string eval is
82 called, that stack frame will show up as "(eval n)", where 'n' is a
83 sequential identifier for every string eval that has happened so
84 far in the program. Passing a "description" parameter lets you
85 override that to something more useful (for instance, Moose
86 overrides the description for accessors to something like "accessor
87 foo at MyClass.pm, line 123").
88 line
90 This lets you override the particular line number that appears in
91 backtraces, much like the "description" option. The default is 1.
92 terse_error
94 Normally, this function appends the source code that failed to
95 compile, and prepends some explanatory text. Setting this option to
96 true suppresses that behavior so you get only the compilation error
97 that Perl actually reported.
98
100 No known bugs.
101 Please report any bugs to GitHub Issues at
103 <https://github.com/doy/eval-closure/issues>.
104
106 • Class::MOP::Method::Accessor
107 This module is a factoring out of code that used to live here
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111 You can find this documentation for this module with the perldoc
112 command.
113 perldoc Eval::Closure
115 You can also look for information at:
117 • MetaCPAN
119 <https://metacpan.org/release/Eval-Closure>
121 • Github
123 <https://github.com/doy/eval-closure>
125 • RT: CPAN's request tracker
127 <http://rt.cpan.org/NoAuth/Bugs.html?Dist=Eval-Closure>
129 • CPAN Ratings
131 <http://cpanratings.perl.org/d/Eval-Closure>
133
135 Based on code from Class::MOP::Method::Accessor, by Stevan Little and
136 the Moose Cabal.
137
139 Jesse Luehrs <doy@tozt.net>
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142 This software is copyright (c) 2016 by Jesse Luehrs.
143 This is free software; you can redistribute it and/or modify it under
145 the same terms as the Perl 5 programming language system itself.
146perl v5.36.0 2023-01-20 Eval::Closure(3)