Eval::Closure(3pm) User Contributed Perl Documentation Eval::Closure(3pm)
NAME
Eval::Closure - safely and cleanly create closures via string eval
VERSION
version 0.14
SYNOPSIS
use Eval::Closure;
my $code = eval_closure(
source => 'sub { $foo++ }',
environment => {
'$foo' => \1,
},
);
warn $code->(); # 1
warn $code->(); # 2
my $code2 = eval_closure(
source => 'sub { $code->() }',
); # dies, $code isn't in scope
DESCRIPTION
String eval is often used for dynamic code generation. For instance,
"Moose" uses it heavily, to generate inlined versions of accessors and
constructors, which speeds code up at runtime by a significant amount.
String eval is not without its issues however - it's difficult to
control the scope it's used in (which determines which variables are in
scope inside the eval), and it's easy to miss compilation errors, since
eval catches them and sticks them in $@ instead.
This module attempts to solve these problems. It provides an
"eval_closure" function, which evals a string in a clean environment,
other than a fixed list of specified variables. Compilation errors are
rethrown automatically.
FUNCTIONS
eval_closure(%args)
This function provides the main functionality of this module. It is
exported by default. It takes a hash of parameters, with these keys
being valid:
source
The string to be evaled. It should end by returning a code
reference. It can access any variable declared in the "environment"
parameter (and only those variables). It can be either a string, or
an arrayref of lines (which will be joined with newlines to produce
the string).
environment
The environment to provide to the eval. This should be a hashref,
mapping variable names (including sigils) to references of the
appropriate type. For instance, a valid value for environment would
be "{ '@foo' => [] }" (which would allow the generated function to
use an array named @foo). Generally, this is used to allow the
generated function to access externally defined variables (so you
would pass in a reference to a variable that already exists).
In perl 5.18 and greater, the environment hash can contain
variables with a sigil of "&". This will create a lexical sub in
the evaluated code (see "The 'lexical_subs' feature" in feature).
Using a "&" sigil on perl versions before lexical subs were
available will throw an error.
alias
If set to true, the coderef returned closes over the variables
referenced in the environment hashref. (This feature requires
Devel::LexAlias.) If set to false, the coderef closes over a
shallow copy of the variables.
If this argument is omitted, Eval::Closure will currently assume
false, but this assumption may change in a future version.
description
This lets you provide a bit more information in backtraces.
Normally, when a function that was generated through string eval is
called, that stack frame will show up as "(eval n)", where 'n' is a
sequential identifier for every string eval that has happened so
far in the program. Passing a "description" parameter lets you
override that to something more useful (for instance, Moose
overrides the description for accessors to something like "accessor
foo at MyClass.pm, line 123").
line
This lets you override the particular line number that appears in
backtraces, much like the "description" option. The default is 1.
terse_error
Normally, this function appends the source code that failed to
compile, and prepends some explanatory text. Setting this option to
true suppresses that behavior so you get only the compilation error
that Perl actually reported.
BUGS
No known bugs.
Please report any bugs to GitHub Issues at
<https://github.com/doy/eval-closure/issues>.
SEE ALSO
• Class::MOP::Method::Accessor
This module is a factoring out of code that used to live here
SUPPORT
You can find this documentation for this module with the perldoc
command.
perldoc Eval::Closure
You can also look for information at:
• MetaCPAN
<https://metacpan.org/release/Eval-Closure>
• Github
<https://github.com/doy/eval-closure>
• RT: CPAN's request tracker
<http://rt.cpan.org/NoAuth/Bugs.html?Dist=Eval-Closure>
• CPAN Ratings
<http://cpanratings.perl.org/d/Eval-Closure>
NOTES
Based on code from Class::MOP::Method::Accessor, by Stevan Little and
the Moose Cabal.
AUTHOR
Jesse Luehrs <doy@tozt.net>
COPYRIGHT AND LICENSE
This software is copyright (c) 2016 by Jesse Luehrs.
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.
perl v5.36.0 2022-11-19 Eval::Closure(3pm)
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