Re: [Boost-users] How strong is PropertyTree JSON support

Subject: Re: [Boost-users] How strong is PropertyTree JSON support
From: Richard Hodges (hodges.r_at_[hidden])
Date: 2019-01-09 02:39:36

On Wed, 9 Jan 2019 at 01:15, Stian Zeljko Vrba via Boost-users <
boost-users_at_[hidden]> wrote:

> You might want to take a look at https://github.com/nlohmann/json
>
>
>
I concur. After looking for a full implementation with a strong and useful
interface I settled on this one.

The provision of _json and _json_pointer literals is a very nice touch.
Also the ability to create JSON objects using initialiser lists allows the
programmer to be almost as expressive as when writing javascript.

>
> ------------------------------
> *From:* Boost-users <boost-users-bounces_at_[hidden]> on behalf of
> Michael Powell via Boost-users <boost-users_at_[hidden]>
> *Sent:* Tuesday, January 8, 2019 6:50:52 PM
> *To:* boost-users_at_[hidden]
> *Cc:* Michael Powell
> *Subject:* [Boost-users] How strong is PropertyTree JSON support
>
> Hello,
>
> I have a requirement to support parsing JSON, and while I could
> potentially pull together a Spirit Qi (or even X3, possibly) based
> grammar, I wonder with all the idiosyncrasies, i.e. particularly
> strings, escape sequences, Unicode, etc, is it worth it.
>
> Then there's the Boost.PropertyTree JSON support, which I think may be
> an adequate fit. However, just how robust is this support when it
> comes to handling some of the nuanced corner cases? The harder ones I
> think are the potential for escape sequences, Unicode, etc, embedded
> within a String.
>
> i.e. https://json.org/
> or, http://es5.github.io/x7.html
>
> It seems with Property Tree there are also these limitations:
>
> <docs>
> The property tree dataset is not typed, and does not support arrays as
> such. Thus, the following JSON / property tree mapping is used:
>
> * JSON objects are mapped to nodes. Each property is a child node.
> * JSON arrays are mapped to nodes. Each element is a child node with
> an empty name. If a node has both named and unnamed child nodes, it
> cannot be mapped to a JSON representation.
> * JSON values are mapped to nodes containing the value. However, all
> type information is lost; numbers, as well as the literals "null",
> "true" and "false" are simply mapped to their string form.
> * Property tree nodes containing both child nodes and data cannot be
> mapped.
> </docs>
>
> It seems to me that much of the limitation is in adapting the
> PropertyTree to the JSON structure, but mostly vice versa. Not quite
> fitting a square peg in a round hole, but coming quite close, I think:
>
> "If a node has both named and unnamed child nodes, it cannot be mapped
> to a JSON representation." We're talking about the mapping from
> PropertyTree to JSON here?
>
> Seems like a potentially problematic issue depending on desired usage,
> 'all type information is lost; numbers, as well as the literals
> "null", "true" and "false" are simply mapped to their string form'.
>
> I'm not sure what "nodes containing both child nodes and data" means?
>
>
> https://www.boost.org/doc/libs/1_69_0/doc/html/property_tree/parsers.html#property_tree.parsers.json_parser
>
> Besides these concerns, I should think a grammar is fairly
> straightforward to construct, if push came to shove. It's either
> living with the Boost.PropertyTree or rolling my own AST, which is not
> outside the realm of possibility for my purposes.
>
> Thoughts? Suggestions?
>
> Thanks!
>
> Michael Powell
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-- 
Richard Hodges
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