0.5 to 0.6
This release introduces a slightly obscure, but backwards-incompatible, change.
In the generic APIs of versions 0.4 and 0.5, fields whose names began
with a "
_" character would have this character removed. This no
longer occurs, as it was both buggy and
0.4 to 0.5
When used with the UTF-8 encoding performance improvements introduced in version 0.11.1.12 of the text package, this release improves aeson's JSON encoding performance by 33% relative to aeson 0.4.
As part of achieving this improvement, an API change was necessary.
fromValue function in the
Data.Aeson.Encode module now uses
the text package's
Builder type instead of the blaze-builder
0.3 to 0.4
Ease of use
complements the longstanding
encode function, and makes the API
New examples make it easier to learn to use the package.
aeson's support for data-type generic programming makes it possible to use JSON encodings of most data types without writing any boilerplate instances.
Thanks to Bas Van Dijk, aeson now supports the two major schemes for doing datatype-generic programming:
the modern mechanism, built into GHC itself
the older mechanism, based on SYB (aka "scrap your boilerplate")
The modern GHC-based generic mechanism is fast and terse: in fact, its
performance is generally comparable in performance to hand-written and
FromJSON instances. To see how to use GHC
generics, refer to
The SYB-based generics support lives in
and is provided mainly for users of GHC older than 7.2. SYB is far
slower (by about 10x) than the more modern generic mechanism. To see
how to use SYB generics, refer to
We switched the intermediate representation of JSON objects from
Data.HashMap, which has improved type conversion performance.
FromJSONfor tuples are between 45% and 70% faster than in 0.3.
This version of aeson makes explicit the decoupling between
identifying an element of a JSON document and converting it to
Haskell. See the
documentation for details.
The normal aeson
decode function performs identification strictly,
but defers conversion until needed. This can result in improved
performance (e.g. if the results of some conversions are never
needed), but at a cost in increased memory consumption.
decode' function performs identification and conversion
immediately. This incurs an up-front cost in CPU cycles, but reduces
reduce memory consumption.