Prework

• I understand and agree to help guide.
• I understand and agree to contributing guide.
• New features take time and effort to create, and they take even more effort to maintain. So if the purpose of the feature is to resolve a struggle you are encountering personally, please consider first posting a "trouble" or "other" issue so we can discuss your use case and search for existing solutions first.

Proposal

I propose that tar_target() takes a new type of format called auto, and if successful, that would become the default. auto would behave in the following way:

• If the output of the target is a data frame, use format = "nanoparquet", which would be a new format that uses nanoparquet to create parquet files. nanoparquet is a zero-dependency parquet reader/writer so targets could take a hard dependency on this package ensuring that it's available to all users.
• If the output is a character vector and all(file.exists(output)) is true, it would use format = "file_fast" (unless trust_object_timestamps is FALSE, in which case it would use "file").
• For all other types "rds". (Unless you'd be willing to add qs as a hard dependency, in which case I'd argue that qs is basically uniformly superior to rds. Alternatively you could use qs if it's installed, but I don't know enough about the architecture of targets to fully understand the consequences of that).

This steers the new user towards high-performance formats while allowing experienced users to continue to pick the best defaults for them.