Re: [boost] [review][JSON] json::value as a vocabulary type

On Fri, Sep 25, 2020 at 9:07 AM Andrzej Krzemienski via Boost wrote:

pt., 25 wrz 2020 o 15:10 Zach Laine via Boost napisał(a):

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On Fri, Sep 25, 2020 at 6:11 AM Mathias Gaunard via Boost wrote:

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On Thu, 24 Sep 2020 at 10:57, Andrzej Krzemienski via Boost wrote:

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My understanding of a "vocabulary type" is that it should be usable

(not

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necessarily with maximum efficiency) for *any* usage. In the case of JSON that would mean that I should be able to represent any value that corresponds to a valid JSON when converted to text. I do not think that json::value can claim that without the ability to serialize arbitrarily big numbers.

I fully agree with this statement. json::value *needs* to support arbitrary numbers. It's incomplete without it. Maybe the author of multiprecision can advise on the best type to use there (gmp or mpfr?).

This is not a reasonable requirement. std::string is the canonical C++ vocabulary type. On 32-bit systems, it cannot represent 5GB-long strings. Depending on platform limitations, it usually cannot even represent more than 2GB-long strings. Computers are limited to finite resources. Putting finite limits on the representation of all kinds of values is normal, not unexpected -- this is especially true of numeric values.

I am wondering. If I have a small web service for generating prime numbers, and I need to return them in a JSON file, is my only option to pass it as string? Prime numbers of this kind are bigger than uint64_t. But they are not as big as 1MB. Is such a use case for a number so unusual that it cannot be stored as a JSON number? Are JSON numbers only good for storing int-based identifiers?

I don't know what an int-based identifier is, but I do know that the use cases for machine-representable ints (that is, and int that is the size of an int, fits in a register, etc.) is >99% and the use cases for a web service that generates prime numbers is <1%. That's what should drive the design. Zach