Function specialization in Printf

General Usage
3

I modified the code according to the referencence like the following:

function my_printf!(io, format::Printf.Format, args::Vararg{Any, N}) where {N} = tuple(args...)
    pos = Printf.format(LOG_DATA_BUFFER, 1, format, args...)
    GC.@preserve LOG_DATA_BUFFER unsafe_write(io, pointer(LOG_DATA_BUFFER), pos - 1)
    return
end

But this does not compile:

ERROR: LoadError: syntax: unexpected "="

where did I do wrong?

ps: I’ve somehow succeed by another way: declaring the my_printf! with @inline. Most of the allocations have been removed, I’ll dig further for the remainings.

I’ve found two things.
First, @inline is a hint to compiler, but it will not force the compiler to do so. I didn’t find a way to do so, and for an example complicated as this one, it will be hard to follow the ideas in this post to make it concrete. My temporary solution is to split the long printf into several short ones, so that they will be inlined.

Second, I’ve used this way in my code:

const FORMAT_STH = Printf.Format(format_string)
function do_sth()
    my_printf!(io, FORMAT_STH, someargs)
end

I suppose in this way, it will all be compiled. However, when there are both %s and %d in the format_string, it will not be specialized. The compiled binary will need to compile the whole my_printf! for this case. Again, my temporary solution is to split the printf into several shorter ones, each containing %s or %d only.