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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 (); |
12 | use Scalar::Util qw(reftype); |
13 | use Try::Tiny; |
14 | |
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15 | =head1 SYNOPSIS |
16 | |
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17 | use Eval::Closure; |
18 | |
19 | my $code = eval_closure( |
20 | source => 'sub { $foo++ }', |
21 | environment => { |
22 | '$foo' => \1, |
23 | }, |
24 | ); |
25 | |
26 | warn $code->(); # 1 |
27 | warn $code->(); # 2 |
28 | |
29 | my $code2 = eval_closure( |
30 | source => 'sub { $code->() }', |
31 | ); # dies, $code isn't in scope |
32 | |
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33 | =head1 DESCRIPTION |
34 | |
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35 | String eval is often used for dynamic code generation. For instance, C<Moose> |
36 | uses it heavily, to generate inlined versions of accessors and constructors, |
37 | which speeds code up at runtime by a significant amount. String eval is not |
38 | without its issues however - it's difficult to control the scope it's used in |
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39 | (which determines which variables are in scope inside the eval), and it's easy |
40 | to miss compilation errors, since eval catches them and sticks them in $@ |
41 | instead. |
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42 | |
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43 | This module attempts to solve these problems. It provides an C<eval_closure> |
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44 | function, which evals a string in a clean environment, other than a fixed list |
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45 | of specified variables. Compilation errors are rethrown automatically. |
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46 | |
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47 | =cut |
48 | |
49 | =func eval_closure(%args) |
50 | |
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51 | This function provides the main functionality of this module. It is exported by |
52 | default. It takes a hash of parameters, with these keys being valid: |
53 | |
54 | =over 4 |
55 | |
56 | =item source |
57 | |
58 | The string to be evaled. It should end by returning a code reference. It can |
59 | access any variable declared in the C<environment> parameter (and only those |
60 | variables). It can be either a string, or an arrayref of lines (which will be |
61 | joined with newlines to produce the string). |
62 | |
63 | =item environment |
64 | |
65 | The environment to provide to the eval. This should be a hashref, mapping |
66 | variable names (including sigils) to references of the appropriate type. For |
67 | instance, a valid value for environment would be C<< { '@foo' => [] } >> (which |
68 | would allow the generated function to use an array named C<@foo>). Generally, |
69 | this is used to allow the generated function to access externally defined |
70 | variables (so you would pass in a reference to a variable that already exists). |
71 | |
72 | =item description |
73 | |
74 | This lets you provide a bit more information in backtraces. Normally, when a |
75 | function that was generated through string eval is called, that stack frame |
76 | will show up as "(eval n)", where 'n' is a sequential identifier for every |
77 | string eval that has happened so far in the program. Passing a C<description> |
78 | parameter lets you override that to something more useful (for instance, |
79 | L<Moose> overrides the description for accessors to something like "accessor |
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80 | foo at MyClass.pm, line 123"). |
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81 | |
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82 | =item line |
83 | |
84 | This lets you override the particular line number that appears in backtraces, |
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85 | much like the C<description> option. The default is 1. |
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86 | |
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87 | =item terse_error |
88 | |
89 | Normally, this function appends the source code that failed to compile, and |
90 | prepends some explanatory text. Setting this option to true suppresses that |
91 | behavior so you get only the compilation error that Perl actually reported. |
92 | |
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93 | =back |
94 | |
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95 | =cut |
96 | |
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97 | sub eval_closure { |
98 | my (%args) = @_; |
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99 | |
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100 | $args{source} = _canonicalize_source($args{source}); |
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101 | _validate_env($args{environment} ||= {}); |
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102 | |
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103 | $args{source} = _line_directive(@args{qw(line description)}) |
104 | . $args{source} |
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105 | if defined $args{description} && !($^P & 0x10); |
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106 | |
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107 | my ($code, $e) = _clean_eval_closure(@args{qw(source environment)}); |
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108 | |
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109 | if (!$code) { |
110 | if ($args{terse_error}) { |
111 | die "$e\n"; |
112 | } |
113 | else { |
114 | croak("Failed to compile source: $e\n\nsource:\n$args{source}") |
115 | } |
116 | } |
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117 | |
118 | return $code; |
119 | } |
120 | |
121 | sub _canonicalize_source { |
122 | my ($source) = @_; |
123 | |
124 | if (defined($source)) { |
125 | if (ref($source)) { |
126 | if (reftype($source) eq 'ARRAY' |
127 | || overload::Method($source, '@{}')) { |
128 | return join "\n", @$source; |
129 | } |
130 | elsif (overload::Method($source, '""')) { |
131 | return "$source"; |
132 | } |
133 | else { |
134 | croak("The 'source' parameter to eval_closure must be a " |
135 | . "string or array reference"); |
136 | } |
137 | } |
138 | else { |
139 | return $source; |
140 | } |
141 | } |
142 | else { |
143 | croak("The 'source' parameter to eval_closure is required"); |
144 | } |
145 | } |
146 | |
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147 | sub _validate_env { |
148 | my ($env) = @_; |
149 | |
150 | croak("The 'environment' parameter must be a hashref") |
151 | unless reftype($env) eq 'HASH'; |
152 | |
153 | for my $var (keys %$env) { |
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154 | croak("Environment key '$var' should start with \@, \%, or \$") |
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155 | unless $var =~ /^([\@\%\$])/; |
156 | croak("Environment values must be references, not $env->{$var}") |
157 | unless ref($env->{$var}); |
158 | } |
159 | } |
160 | |
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161 | sub _line_directive { |
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162 | my ($line, $description) = @_; |
163 | |
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164 | $line = 1 unless defined($line); |
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165 | |
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166 | return qq{#line $line "$description"\n}; |
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167 | } |
168 | |
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169 | sub _clean_eval_closure { |
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170 | my ($source, $captures) = @_; |
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171 | |
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172 | my @capture_keys = sort keys %$captures; |
173 | |
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174 | if ($ENV{EVAL_CLOSURE_PRINT_SOURCE}) { |
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175 | _dump_source(_make_compiler_source($source, @capture_keys)); |
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176 | } |
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177 | |
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178 | my ($compiler, $e) = _make_compiler($source, @capture_keys); |
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179 | my $code; |
180 | if (defined $compiler) { |
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181 | $code = $compiler->(@$captures{@capture_keys}); |
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182 | } |
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183 | |
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184 | if (defined($code) && (!ref($code) || ref($code) ne 'CODE')) { |
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185 | $e = "The 'source' parameter must return a subroutine reference, " |
186 | . "not $code"; |
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187 | undef $code; |
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188 | } |
189 | |
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190 | return ($code, $e); |
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191 | } |
192 | |
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193 | sub _make_compiler { |
194 | my $source = _make_compiler_source(@_); |
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195 | |
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196 | return @{ _clean_eval($source) }; |
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197 | } |
198 | |
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199 | $Eval::Closure::SANDBOX_ID = 0; |
200 | |
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201 | sub _clean_eval { |
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202 | $Eval::Closure::SANDBOX_ID++; |
203 | return eval <<EVAL; |
204 | package Eval::Closure::Sandbox_$Eval::Closure::SANDBOX_ID; |
205 | local \$@; |
206 | local \$SIG{__DIE__}; |
207 | my \$compiler = eval \$_[0]; |
208 | my \$e = \$@; |
209 | [ \$compiler, \$e ]; |
210 | EVAL |
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211 | } |
212 | |
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213 | sub _make_compiler_source { |
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214 | my ($source, @capture_keys) = @_; |
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215 | my $i = 0; |
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216 | return join "\n", ( |
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217 | 'sub {', |
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218 | (map { |
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219 | 'my ' . $_ . ' = ' . substr($_, 0, 1) . '{$_[' . $i++ . ']};' |
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220 | } @capture_keys), |
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221 | $source, |
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222 | '}', |
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223 | ); |
224 | } |
225 | |
226 | sub _dump_source { |
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227 | my ($source) = @_; |
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228 | |
229 | my $output; |
230 | if (try { require Perl::Tidy }) { |
231 | Perl::Tidy::perltidy( |
232 | source => \$source, |
233 | destination => \$output, |
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234 | argv => [], |
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235 | ); |
236 | } |
237 | else { |
238 | $output = $source; |
239 | } |
240 | |
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241 | warn "$output\n"; |
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242 | } |
243 | |
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244 | =head1 BUGS |
245 | |
246 | No known bugs. |
247 | |
248 | Please report any bugs through RT: email |
249 | C<bug-eval-closure at rt.cpan.org>, or browse to |
250 | L<http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Eval-Closure>. |
251 | |
252 | =head1 SEE ALSO |
253 | |
254 | =over 4 |
255 | |
256 | =item * L<Class::MOP::Method::Accessor> |
257 | |
258 | This module is a factoring out of code that used to live here |
259 | |
260 | =back |
261 | |
262 | =head1 SUPPORT |
263 | |
264 | You can find this documentation for this module with the perldoc command. |
265 | |
266 | perldoc Eval::Closure |
267 | |
268 | You can also look for information at: |
269 | |
270 | =over 4 |
271 | |
272 | =item * AnnoCPAN: Annotated CPAN documentation |
273 | |
274 | L<http://annocpan.org/dist/Eval-Closure> |
275 | |
276 | =item * CPAN Ratings |
277 | |
278 | L<http://cpanratings.perl.org/d/Eval-Closure> |
279 | |
280 | =item * RT: CPAN's request tracker |
281 | |
282 | L<http://rt.cpan.org/NoAuth/Bugs.html?Dist=Eval-Closure> |
283 | |
284 | =item * Search CPAN |
285 | |
286 | L<http://search.cpan.org/dist/Eval-Closure> |
287 | |
288 | =back |
289 | |
290 | =head1 AUTHOR |
291 | |
292 | Jesse Luehrs <doy at tozt dot net> |
293 | |
294 | Based on code from L<Class::MOP::Method::Accessor>, by Stevan Little and the |
295 | Moose Cabal. |
296 | |
297 | =cut |
298 | |
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299 | 1; |