[phobos] For review: Improvements to std.variant and std.json

[Lutger Blijdestijn]

Hi, I just wanted to comment on the dson file format.

While perhaps less efficient, the mongodb nosql database also uses a binary
json (bson) format to store data. It implements some extra types though. I
suggest that if you want to implement binary json, to seriously consider
adopting bson instead:

http://bsonspec.org/

<http://bsonspec.org/>
2010/11/20 Robert Jacques <sandford at jhu.edu>

> I have been working on a re-write of std.json. The purpose was to fix
> implementation bugs, better conform to the spec, provide a lightweight
> tokenizer (Sean) and to use an Algebraic type (Andrei) for JSON values. In
> the progress of doing this, I made my parser 2x faster and updated/fixed a
> bunch of issues with VariantN in order to fully support Algebraic types.
> Both of these libraries are at a solid beta level, so I'd like to get some
> feedback, and provide a patch for those being held back by the problems with
> Algebraic. The code and docs are available at:
> https://jshare.johnshopkins.edu/rjacque2/public_html/. These files were
> written against DMD 2.050 and both depend on some patches currently in
> bugzilla (see the top of each file or below)
>
> Summary of Variant changes:
> * Depends on Issue 5155's patch
> * VariantN now properly supports types defined using "This".
> * Additional template constraints and acceptance of implicit converters in
> opAssign and ctor. i.e. if an Algebraic type supports reals, you can now
> assign an int to it.
> * Updated to using opBinary/opBinaryRight/opOpAssign. This adds right
> support to several functions and is now generated via compile time
> reflection + mixins: i.e. Algebraic types of user defined types should work,
> etc.
> * Added opIn support, though it currently on works for AAs.
> * Added opIndexOpAssign support.
> * Added opDispatch as an alternative indexing method. This allows Variants
> of type Variant[string] to behave like prototype structs: i.e. var.x = 5;
> instead of var["x"] = 5;
>
> Notes:
> * There's an bugzilla issue requesting opCall support in Variant. While I
> can see the usefulness, syntactically this clashes with the ctor. Should
> this issue be closed or should a method be used as an opCall surrogate?
> * Could someone explain to me the meaning/intension of "Future additions to
> Algebraic will allow compile-time checking that all possible types are
> handled by user code, eliminating a large class of errors." Is this
> something akin to final switch support?
>
> Summary of JSON changes:
> * Depends on the Variant improvements.
> * Depends on Issue 5233's patch
> * Depends on Issue 5236's patch
> * Issue 5232's patch is also recommended
> * The integer type was removed: JSON doesn't differentiate between floating
> and integral numbers. Internally, reals are used and on systems with 80-bit
> support, this encompasses all integral types.
> * UTF escape characters are now correctly support.
> * All routines/types were encapsulated in a JSON struct for name space
> reasons.
> * An Algebraic type is used for JSON values, with
> serialization/de-serialization routines as free methods.
> * Serialization/de-serialization centers around a set of input/output range
> to/from token range routines, with separate parser/writer routines.
> * Values can be written in either a concise (default) or pretty printed
> format. (i.e. indented with line returns)
> * Convenience toString and toStringHR routines exist.
> * Simple Type to/from json routines exist, but are marked as to be
> re-evaluated pending std.serialization.
> * I've implemented a binary format customized for JSON. Besides preserving
> numeric precision (i.e. 80-bit reals), I found it gave slightly smaller file
> size (~20%) and 2-3x parsing performance for a large numeric dataset of
> mine. I'm not sure if it's worth-while on the whole, so I'd appreciate
> feedback.
>
> Notes:
> * Does anyone have a suggestion of a good way to attach methods to an
> Algebraic type? And if we can, should we?
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