Can we have a json_view class like std::string_view?

[qduyang]

• Describe the feature in as much detail as possible.
  As copy a json would have many allocations, it would nice to have a view class like std::string_view for performance's sake.

[nlohmann]

Could you provide more information or examples?

[qduyang]

The use case is that, there is an immutable template nlohmann::json object as below, and there would have thousands of concurrent access to it.

{
   "id": 1234567,
   "data": [{"price": 123, "quantity": 1} , {"price": 123, "quantity": 1}
}

Each access will

• make copy of the template
• update the "id" field only
• dump it to string
• then send the generated string to some other applications.

I want to avoid the the copy in the first step.
If there is a view class which could generate a joint view from the "data" field (in the immutable template) and a new "id" field, we can avoid the allocations for duplicates "data".
The general concept is to have a json_view that creates a jointly view from multiple nlohmann::json objects without any extra allocations.
The idea is stolen from https://www.boost.org/doc/libs/1_67_0/libs/mpl/doc/refmanual/joint-view.html
And there are also some other views, https://www.boost.org/doc/libs/1_67_0/libs/mpl/doc/refmanual/views.html

(The concept is not same as std::string_view class, but the non-owning concept would be similar)

[nlohmann]

I think I understand the issue, but I am skeptical whether an implementation to this library is possible (or at least: possible without too much effort).

[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.

[qduyang]

One premature thinking is to have a json_view class which accepts const JSON references parameters to construct new JSONs. In this case, we avoid data copying, but leave the referred objects' lifetime management to the user, and It will cause undefined behavior if use incorrectly.
I will find time to read the code, and see if I could give you some suggestion.

[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.