Custom formatting of user defined types

[rajnishdahiya]

BINLOG_ADAPT_STRUCT allows logging used defined types and their members. However, the user has no control over the formatting when the type is pretty-printed.

One possibility is to simply do the formatting on the producer side, but that is less than ideal for performance.

What's the best way to add support for custom formatting of user defined types, preferably via a standard interface like operator<<?

[erenon]

To pretty print custom structures, there are two options:

• Log them as string: works, but hurts performance and make it more difficult to parse the logfile programmatically
• Bake your own bread, and change PrettyPrinter::printStruct: https://github.com/morganstanley/binlog/blob/main/include/binlog/PrettyPrinter.cpp#L117. There you can use whatever mechanism to pretty print the object (see the current implementation for examples)

[rajnishdahiya]

Your suggestion seems to pretty-fy adapted structs.
I am looking to avoid adapting all together as it can get quite messy for my logging needs, e.g. my type might have a vector and I want to log only 1st few entries of it. Also in my project it's advised to have a standard logging mechanism (implementing operator << or fmt::format), I was hoping to use same infrastructure.

I didn't look deeper but will something like below work?
Have a dedicated thread for consuming from queues. And writing out directly to text format, i.e. TextOutputStream.

1. Pass (log) a pointer as binlog::address or void*, along with some tag/category (saying it's a user_defined_type Type1)
2. Customize serialization (mserialize, ToStringVisitor etc)
3. check for special tag/category, if yes then extract pointer from buffer, cast it to Type1 and use already defined fmt::format, operator << etc for that type to serialize.
   I am aware of potential issues of using dangling pointers and logging outdated object state here, but let's assume that is acceptable.