| … | |
… | |
| 347 | future, global hooks might get installed that influence C<decode> and are |
347 | future, global hooks might get installed that influence C<decode> and are |
| 348 | enabled by this setting. |
348 | enabled by this setting. |
| 349 | |
349 | |
| 350 | If C<$enable> is false, then the C<allow_blessed> setting will decide what |
350 | If C<$enable> is false, then the C<allow_blessed> setting will decide what |
| 351 | to do when a blessed object is found. |
351 | to do when a blessed object is found. |
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352 | |
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353 | =item $json = $json->filter_json_object ([$coderef]) |
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354 | |
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355 | When C<$coderef> is specified, it will be called from C<decode> each |
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356 | time it decodes a JSON object. The only argument is a reference to the |
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357 | newly-created hash. If the code references returns a single scalar (which |
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358 | need not be a reference), this value (i.e. a copy of that scalar to avoid |
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359 | aliasing) is inserted into the deserialised data structure. If it returns |
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360 | an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the |
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361 | original deserialised hash will be inserted. This setting can slow down |
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362 | decoding considerably. |
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363 | |
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364 | When C<$coderef> is omitted or undefined, C<decode> will not change the |
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365 | deserialised hash in any way. This is maximally fast. |
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366 | |
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367 | Example, convert all JSON objects into the integer 5: |
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368 | |
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369 | my $js = JSON::XS->new->filter_json_object (sub { 5 }); |
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370 | # returns [5] |
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371 | $js->decode ('[{}]') |
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372 | # throw an exception because allow_nonref is not enabled: |
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373 | $js->decode ('{"a":1, "b":2}'); |
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374 | |
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375 | =item $json = $json->filter_json_single_key_object ([$coderef]) |
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376 | |
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377 | Works like C<filter_json_object>, but is only called for JSON objects |
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378 | having only a single key. |
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379 | |
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380 | This C<$coderef> is called before the one specified via |
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381 | C<filter_json_object>, if any. If it returns something, that will be |
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382 | inserted into the data structure. If it returns nothing, the callback |
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383 | from C<filter_json_object> will be called next. If you want to force |
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384 | insertion of single-key objects even in the presence of a mutating |
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385 | C<filter_json_object> callback, simply return the passed hash. |
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386 | |
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387 | As this callback gets called less often then the C<filter_json_object> |
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388 | one, decoding speed will not usually suffer as much. Therefore, single-key |
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389 | objects make excellent targets to serialise Perl objects into, especially |
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390 | as single-key JSON objects are as close to the type-tagged value concept |
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391 | as JSON gets (its basically an ID/VALUE tuple). Of course, JSON does not |
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392 | support this in any way, so you need to make sure your data never looks |
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393 | like a serialised Perl hash. |
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394 | |
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395 | Typical names for the single object key are C<__class_whatever__>, or |
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396 | C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even |
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397 | things like C<__class_md5sum(classname)__>, to reduce the risk of clashing |
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398 | with real hashes. |
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399 | |
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400 | Example, decode JSON objects of the form C<< { "__widget__" => <id> } >> |
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401 | into the corresponding C<< $WIDGET{<id>} >> object: |
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402 | |
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403 | # return whatever is in $WIDGET{5}: |
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404 | JSON::XS |
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405 | ->new |
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406 | ->filter_json_single_key_object (sub { |
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407 | exists $_[0]{__widget__} |
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408 | ? $WIDGET{ $_[0]{__widget__} } |
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409 | : () |
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410 | }) |
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411 | ->decode ('{"__widget__": 5') |
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412 | |
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413 | # this can be used with a TO_JSON method in some "widget" class |
|
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414 | # for serialisation to json: |
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415 | sub WidgetBase::TO_JSON { |
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416 | my ($self) = @_; |
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417 | |
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418 | unless ($self->{id}) { |
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419 | $self->{id} = ..get..some..id..; |
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420 | $WIDGET{$self->{id}} = $self; |
|
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421 | } |
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422 | |
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423 | { __widget__ => $self->{id} } |
|
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424 | } |
| 352 | |
425 | |
| 353 | =item $json = $json->shrink ([$enable]) |
426 | =item $json = $json->shrink ([$enable]) |
| 354 | |
427 | |
| 355 | Perl usually over-allocates memory a bit when allocating space for |
428 | Perl usually over-allocates memory a bit when allocating space for |
| 356 | strings. This flag optionally resizes strings generated by either |
429 | strings. This flag optionally resizes strings generated by either |
