Question: Attribute Annotations

I'm interested in the "struct reflection" features of Boost.Hana. I think that this part of Boost.Hana is especially suited for all kinds of serialization/marshalling + deserialization/unmarshalling (file reading/writing, network/API protocols, database access, etc.).

Other languages offer a functionality to "annotate" member variables:
- Python and Java have "@" (used for Hibernate, Jackson, etc.)
- In Go you can use something like `json:"var_name"` (example: https://play.golang.org/p/BMeR8p1cKf)
- etc.

Use cases include JSON/XML attribute names (API naming conventions can be different to variable naming), parser information (i.e. CSV column names, XPath for XML to struct parsing), optional/required/versioning information for formats like Protocol Buffers or Flatbuffers, or database information ("PRIMARY KEY", "UNIQUE", "NOT NULL", etc. - this way SELECT, CREATE TABLE statements, etc. could be automatically generated from the struct definition at compile time - see https://github.com/rbock/sqlpp11).

Is there already a way to do something like this (i.e. generic additional attribute "tags") or (if that's not the case) are there any plans to extend Boost.Hana?

Start with Boost.Hana's struct reflection features and the annotation use cases described in the issue. Determine whether generic member attributes or tags already exist; otherwise, the work would need a maintainer decision on the design and scope of an extension.

Written by the indexing model from the issue text.