Macro that adds object to array in compile time?

Question

I want to create a list of static compile time generated variables. That is, when the program starts, they are already there and I don't need to mutate it.

Currently I'm doing like this:

pub type ProfilerInfo = (&'static str, &'static str);

pub const Fps: ProfilerInfo = ("fps", "Frames Per Second");
pub const DecodingElapsed: ProfilerInfo = ("det", "Decoding Elapsed Time");
pub const DecodedPerSec: ProfilerInfo = ("dps", "Decoded Per Second");
pub const BytesPerSec: ProfilerInfo = ("bps", "Bytes Per Second");

pub const ALL_VARIABLES: &'static [&'static ProfilerInfo] = &[&Fps, &DecodingElapsed, &DecodedPerSec, &BytesPerSec];

however this is error prone, I could forget to add one of the variables on the list ALL_VARIABLES.

Is there a way to create a macro that creates a ProfilerInfo and adds to ALL_VARIABLES?

Context: why I need this? Well, this list is to be returned by the command line like this my_program --list-variables, so it's nice for it to be done when the app starts.

I don't think it's possible with an array like I did on the top but maybe with a Vec?

Deadbeef · Accepted Answer · 2021-06-28 01:52:52Z

1

You want a macro that creates the ALL_VARIABLES static slice for you.

pub type ProfilerInfo = (&'static str, &'static str);

macro_rules! profiler_variables {
    ($(pub const $id:ident: ProfilerInfo = $rhs:expr;)*) => {
        $(
            pub const $id: ProfilerInfo = $rhs;
        )*
        pub const ALL_VARIABLES: &'static [&'static ProfilerInfo] = &[$(&$id),*];
    }
}

profiler_variables! {
    pub const Fps: ProfilerInfo = ("fps", "Frames Per Second");
    pub const DecodingElapsed: ProfilerInfo = ("det", "Decoding Elapsed Time");
    pub const DecodedPerSec: ProfilerInfo = ("dps", "Decoded Per Second");
    pub const BytesPerSec: ProfilerInfo = ("bps", "Bytes Per Second");
}

fn main() {
    for (name, descr) in ALL_VARIABLES.iter() {
        println!("Variable: {}, description: {}", name, descr)
    }
}

Output:

Variable: fps, description: Frames Per Second
Variable: det, description: Decoding Elapsed Time
Variable: dps, description: Decoded Per Second
Variable: bps, description: Bytes Per Second

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answered Jun 28, 2021 at 1:52

Deadbeef

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Poperton Over a year ago

I didn't know I could match with patterns on macros, thanks

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