++ed by:
4 non-PAUSE users
Author image Jesse Luehrs
and 1 contributors


Eval::Closure - safely and cleanly create closures via string eval


version 0.04


  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


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 can be quite slow, especially if doing a large number of evals.

This module attempts to solve both of those problems. It provides an eval_closure function, which evals a string in a clean environment, other than a fixed list of specified variables. It also caches the result of the eval, so that doing repeated evals of the same source, even with a different environment, will be much faster (but note that the description is part of the string to be evaled, so it must also be the same (or non-existent) if caching is to work properly).



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:


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).


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).


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").


This lets you override the particular line number that appears in backtraces, much like the description option. The default is 1.


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.


No known bugs.

Please report any bugs through RT: email bug-eval-closure at rt.cpan.org, or browse to http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Eval-Closure.


You can find this documentation for this module with the perldoc command.

    perldoc Eval::Closure

You can also look for information at:


Jesse Luehrs <doy at tozt dot net>

Based on code from Class::MOP::Method::Accessor, by Stevan Little and the Moose Cabal.



This software is copyright (c) 2011 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.