Handlers

As we've already seen, Handlers can be used to write log messages to different IO types. More specifically, handlers are parameterized types that describe the relationship of how Formatter and IO types are used to take a Record (a kind of specified Dict) -> convert it to a String with the Formatter and write that to an IO type.

In the simplest case a Handler definition would like:

mutable struct MyHandler{F<:Formatter, O<:IO} <: Handler{F, O}
    fmt::F
    io::O
end

function emit(handler::MyHandler{F, O}, rec::Record) where {F<:Formatter, O<:IO}
    str = Memento.format(handler.fmt, rec)
    println(handler.io, str)
    flush(handler.io)
end

However, under some circumstances it may be necessary to customize this behaviour based on the Formatter, IO or Record types being used. For example, if you'd like to use the Syslog IO type from Syslogs.jl you'll need topass in an extra level argument to its println so we special case this like so:

using Syslogs

function emit(handler::MyHandler{F, O}, rec::Record) where {F<:Formatter, O<:Syslog}
    str = Memento.format(handler.fmt, rec)
    println(handler.io, rec.level, str)
    flush(handler.io)
end