Function flexi_logger::opt_format

pub fn opt_format(
    w: &mut dyn Write, 
    now: &mut DeferredNow, 
    record: &Record
) -> Result<(), Error>

A logline-formatter that produces log lines with timestamp and file location, like
[2016-01-13 15:25:01.640870 +01:00] INFO [src/foo/bar:26] Task successfully read from conf.json

Errors

See std::write