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1 | package Eval::Closure; |
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2 | use strict; |
3 | use warnings; |
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4 | use Sub::Exporter -setup => { |
5 | exports => [qw(eval_closure)], |
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6 | groups => { default => [qw(eval_closure)] }, |
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7 | }; |
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8 | # ABSTRACT: safely and cleanly create closures via string eval |
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9 | |
10 | use Carp; |
11 | use overload (); |
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12 | use Memoize; |
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13 | use Scalar::Util qw(reftype); |
14 | use Try::Tiny; |
15 | |
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16 | =head1 SYNOPSIS |
17 | |
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18 | use Eval::Closure; |
19 | |
20 | my $code = eval_closure( |
21 | source => 'sub { $foo++ }', |
22 | environment => { |
23 | '$foo' => \1, |
24 | }, |
25 | ); |
26 | |
27 | warn $code->(); # 1 |
28 | warn $code->(); # 2 |
29 | |
30 | my $code2 = eval_closure( |
31 | source => 'sub { $code->() }', |
32 | ); # dies, $code isn't in scope |
33 | |
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34 | =head1 DESCRIPTION |
35 | |
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36 | String eval is often used for dynamic code generation. For instance, C<Moose> |
37 | uses it heavily, to generate inlined versions of accessors and constructors, |
38 | which speeds code up at runtime by a significant amount. String eval is not |
39 | without its issues however - it's difficult to control the scope it's used in |
40 | (which determines which variables are in scope inside the eval), and it can be |
41 | quite slow, especially if doing a large number of evals. |
42 | |
43 | This module attempts to solve both of those problems. It provides an |
44 | C<eval_closure> function, which evals a string in a clean environment, other |
45 | than a fixed list of specified variables. It also caches the result of the |
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46 | eval, so that doing repeated evals of the same source, even with a different |
47 | environment, will be much faster (but note that the description is part of the |
48 | string to be evaled, so it must also be the same (or non-existent) if caching |
49 | is to work properly). |
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50 | |
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51 | =cut |
52 | |
53 | =func eval_closure(%args) |
54 | |
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55 | This function provides the main functionality of this module. It is exported by |
56 | default. It takes a hash of parameters, with these keys being valid: |
57 | |
58 | =over 4 |
59 | |
60 | =item source |
61 | |
62 | The string to be evaled. It should end by returning a code reference. It can |
63 | access any variable declared in the C<environment> parameter (and only those |
64 | variables). It can be either a string, or an arrayref of lines (which will be |
65 | joined with newlines to produce the string). |
66 | |
67 | =item environment |
68 | |
69 | The environment to provide to the eval. This should be a hashref, mapping |
70 | variable names (including sigils) to references of the appropriate type. For |
71 | instance, a valid value for environment would be C<< { '@foo' => [] } >> (which |
72 | would allow the generated function to use an array named C<@foo>). Generally, |
73 | this is used to allow the generated function to access externally defined |
74 | variables (so you would pass in a reference to a variable that already exists). |
75 | |
76 | =item description |
77 | |
78 | This lets you provide a bit more information in backtraces. Normally, when a |
79 | function that was generated through string eval is called, that stack frame |
80 | will show up as "(eval n)", where 'n' is a sequential identifier for every |
81 | string eval that has happened so far in the program. Passing a C<description> |
82 | parameter lets you override that to something more useful (for instance, |
83 | L<Moose> overrides the description for accessors to something like "accessor |
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84 | foo at MyClass.pm, line 123"). |
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85 | |
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86 | =item line |
87 | |
88 | This lets you override the particular line number that appears in backtraces, |
89 | much like the description option. The default is "1". |
90 | |
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91 | =item terse_error |
92 | |
93 | Normally, this function appends the source code that failed to compile, and |
94 | prepends some explanatory text. Setting this option to true suppresses that |
95 | behavior so you get only the compilation error that Perl actually reported. |
96 | |
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97 | =back |
98 | |
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99 | =cut |
100 | |
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101 | sub eval_closure { |
102 | my (%args) = @_; |
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103 | |
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104 | $args{source} = _canonicalize_source($args{source}); |
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105 | _validate_env($args{environment} ||= {}); |
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106 | |
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107 | $args{source} = _line_directive(@args{qw(line description)}) . $args{source} |
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108 | if defined $args{description}; |
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109 | |
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110 | my ($code, $e) = _clean_eval_closure(@args{qw(source environment)}); |
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111 | |
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112 | if (!$code) { |
113 | if ($args{terse_error}) { |
114 | die "$e\n"; |
115 | } |
116 | else { |
117 | croak("Failed to compile source: $e\n\nsource:\n$args{source}") |
118 | } |
119 | } |
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120 | |
121 | return $code; |
122 | } |
123 | |
124 | sub _canonicalize_source { |
125 | my ($source) = @_; |
126 | |
127 | if (defined($source)) { |
128 | if (ref($source)) { |
129 | if (reftype($source) eq 'ARRAY' |
130 | || overload::Method($source, '@{}')) { |
131 | return join "\n", @$source; |
132 | } |
133 | elsif (overload::Method($source, '""')) { |
134 | return "$source"; |
135 | } |
136 | else { |
137 | croak("The 'source' parameter to eval_closure must be a " |
138 | . "string or array reference"); |
139 | } |
140 | } |
141 | else { |
142 | return $source; |
143 | } |
144 | } |
145 | else { |
146 | croak("The 'source' parameter to eval_closure is required"); |
147 | } |
148 | } |
149 | |
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150 | sub _validate_env { |
151 | my ($env) = @_; |
152 | |
153 | croak("The 'environment' parameter must be a hashref") |
154 | unless reftype($env) eq 'HASH'; |
155 | |
156 | for my $var (keys %$env) { |
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157 | croak("Environment key '$var' should start with \@, \%, or \$") |
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158 | unless $var =~ /^([\@\%\$])/; |
159 | croak("Environment values must be references, not $env->{$var}") |
160 | unless ref($env->{$var}); |
161 | } |
162 | } |
163 | |
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164 | sub _line_directive { |
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165 | my ($line, $description) = @_; |
166 | |
167 | $line = 1 if !defined($line); |
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168 | |
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169 | return qq{#line $line "$description"\n}; |
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170 | } |
171 | |
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172 | sub _clean_eval_closure { |
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173 | my ($source, $captures) = @_; |
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174 | |
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175 | if ($ENV{EVAL_CLOSURE_PRINT_SOURCE}) { |
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176 | _dump_source(_make_compiler_source(@_)); |
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177 | } |
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178 | |
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179 | my @capture_keys = sort keys %$captures; |
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180 | my ($compiler, $e) = _make_compiler($source, @capture_keys); |
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181 | my $code; |
182 | if (defined $compiler) { |
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183 | $code = $compiler->(@$captures{@capture_keys}); |
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184 | } |
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185 | |
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186 | if (defined($code) && (!ref($code) || ref($code) ne 'CODE')) { |
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187 | $e = "The 'source' parameter must return a subroutine reference, " |
188 | . "not $code"; |
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189 | undef $code; |
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190 | } |
191 | |
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192 | return ($code, $e); |
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193 | } |
194 | |
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195 | sub _make_compiler { |
196 | local $@; |
197 | local $SIG{__DIE__}; |
198 | my $compiler = eval _make_compiler_source(@_); |
199 | my $e = $@; |
200 | return ($compiler, $e); |
201 | } |
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202 | memoize('_make_compiler'); |
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203 | |
204 | sub _make_compiler_source { |
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205 | my ($source, @capture_keys) = @_; |
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206 | my $i = 0; |
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207 | return join "\n", ( |
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208 | 'sub {', |
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209 | (map { |
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210 | 'my ' . $_ . ' = ' . substr($_, 0, 1) . '{$_[' . $i++ . ']};' |
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211 | } @capture_keys), |
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212 | $source, |
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213 | '}', |
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214 | ); |
215 | } |
216 | |
217 | sub _dump_source { |
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218 | my ($source) = @_; |
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219 | |
220 | my $output; |
221 | if (try { require Perl::Tidy }) { |
222 | Perl::Tidy::perltidy( |
223 | source => \$source, |
224 | destination => \$output, |
225 | ); |
226 | } |
227 | else { |
228 | $output = $source; |
229 | } |
230 | |
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231 | warn "$output\n"; |
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232 | } |
233 | |
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234 | =head1 BUGS |
235 | |
236 | No known bugs. |
237 | |
238 | Please report any bugs through RT: email |
239 | C<bug-eval-closure at rt.cpan.org>, or browse to |
240 | L<http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Eval-Closure>. |
241 | |
242 | =head1 SEE ALSO |
243 | |
244 | =over 4 |
245 | |
246 | =item * L<Class::MOP::Method::Accessor> |
247 | |
248 | This module is a factoring out of code that used to live here |
249 | |
250 | =back |
251 | |
252 | =head1 SUPPORT |
253 | |
254 | You can find this documentation for this module with the perldoc command. |
255 | |
256 | perldoc Eval::Closure |
257 | |
258 | You can also look for information at: |
259 | |
260 | =over 4 |
261 | |
262 | =item * AnnoCPAN: Annotated CPAN documentation |
263 | |
264 | L<http://annocpan.org/dist/Eval-Closure> |
265 | |
266 | =item * CPAN Ratings |
267 | |
268 | L<http://cpanratings.perl.org/d/Eval-Closure> |
269 | |
270 | =item * RT: CPAN's request tracker |
271 | |
272 | L<http://rt.cpan.org/NoAuth/Bugs.html?Dist=Eval-Closure> |
273 | |
274 | =item * Search CPAN |
275 | |
276 | L<http://search.cpan.org/dist/Eval-Closure> |
277 | |
278 | =back |
279 | |
280 | =head1 AUTHOR |
281 | |
282 | Jesse Luehrs <doy at tozt dot net> |
283 | |
284 | Based on code from L<Class::MOP::Method::Accessor>, by Stevan Little and the |
285 | Moose Cabal. |
286 | |
287 | =cut |
288 | |
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289 | 1; |