input_adapter not user extensible

[abrownsword]

I need to implement a slight variation on one of the standard input adapters, but I have no way to implement the input_adapter_protocol and then connect it to the detail::input_adapter. This is basically equivalent to my earlier issue about making output_adapter extensible (#1534 ) as well.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[jzakrzewski]

Would be a great thing to have!

[abrownsword]

Would like to keep this issue alive and see it addressed. Input data very often comes from sources which are not std::istream or in-memory strings.

[nlohmann]

This may be fixed in #1950.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[FrancoisChabot]

Here's how I think this should look:

I suggest adding the following overload to the parse function(s):

template<typename IteratorType>
json parse(IteratorType begin, IteratorType end, bool strict);

Internally, this would check if std::iterator_traits<IteratorType>::value_type is int8_t , uint8_t, or wchar_t, and properly instantiate a matching input adapter.

A user-defined input would just be a matter of creating a user-defined iterator.

I will also reiterate my opinion that the brace-enclosed syntax should be deprecated, as its existence is predicated on the implicit construction of a library-internal type, which should not be part of the documentation.

char* raw = ...;
std::size_t len = ...;
auto data = json::parse({raw, len});   // Current, effectively undocumented.
auto data = json::parse(raw, raw + len); // new, better syntax