Re: [boost] New JSON library from the maker of Beast!

On 9/23/19 6:11 PM, Vinnie Falco wrote:

On Mon, Sep 23, 2019 at 8:58 AM Bjorn Reese via Boost wrote:

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...online parser... A push parser (SAX)... A tree parser (DOM)

I have no experience with these terms other than occasionally coming across them in my Google searching adventures. The parsers that I have written take as input one or more buffers of contiguous characters, and produce as "output" a series of calls to abstract member functions which are implemented in the derived class. These calls represent tokens or events, such as "key string", "object begin", "array end". So what would we call this in the taxonomy above?

So if I understand your model correctly, it parses as many token as possible, and each token results in a callback. When you reach the end of the buffer, you manually suspend parsing and resume when more data is fed into it. That sounds like a variation of a push parser. It may be easier to understand the parser models in C++ terms, although these terms do not accurately cover the parser models. A pull parser is equivalent to a forward iterator. The user tells it when to advance to the next element. A pull parser usually has a richer interface than a C++ iterator because we are iterating over heterogenous elements. We therefore need to query multiple attributes of the current element, such as * The type of the current element (e.g. integer, string, start of array) * The converted value (e.g. text-to-integer conversion, or JSON string to UTF-8 string conversion) * The unconverted value (a string view of the input corresponding to the current value) A push parser is equivalent to a loop with a visitor. The loop traverses the entire input, and for each recognized element it calls the visitor. Assuming you already have a rich iterator, then it is straight-forward to use this for the loop and call a visitor in each iteration. That is, push parsers are easily build on top of pull parsers. You can find a simple example of this here: https://github.com/breese/trial.protocol/tree/develop/example/json/push_pars... A more elaborate example shows an alternative implementation of boost::property_tree JSON parser using a pull parser: https://github.com/breese/trial.protocol/blob/develop/example/json/property_...