pwm_macro.rs

pub trait Pins {
    const C1: bool;
    const C2: bool;
    const C3: bool;
    type Channels;
}

macro_rules! impl_pins {
    // Expands to a struct that implements the Pins trait
    // The syntax is a bit strange, but it should be generated by another
    // macro anyway, so it's not a huge issue.
    //
    // 4 channels have to be specified as a comma separated list of $channel(...)
    // Each active channel should have $pin, $channel, true; inside the parens
    // Each inactive channel should have ;$unused_type, false inside
    (
        $( $channel:ident(
                $($channel_:ty, $pin:ty, $true:expr)?
                ; $($unused_type:ty, $false:expr)?
            )
         ),*
    ) => {
        // Expand to a struct containing every active channel
        impl Pins for ( $( $( $pin )? $( $unused_type )?),* ) {
            // Set the channel active booleans to true or false depending on activity
            $(
                $(const $channel: bool = $true;)?
                $(const $channel: bool = $false;)?
            )*
            // Create the Channels type
            type Channels = ( $( $($channel_,)? )* );
        }
    }
}

macro_rules! expand_pwm_map {
    () => {};
    ( ($channel:ty,$pin:ty), $( ($rest_channel:ty, $rest_pin:ty) ),* ) => {
        impl_pins!(
            $channel($pin, $channel, true;),
            expand_pwm_map!( $( ($rest_channel, $rest_ty) ),* )
        );
        impl_pins!(
            $channel($pin, $channel, true;),
            expand_pwm_map!( $( ($rest_channel, $rest_ty) ),* )
        );
    }
}

macro_rules! pwm_map {
    ($pin1:ty, $pin2:ty, $pin3:ty, $pin4:ty) => {
    }
}

pub struct C1;
pub struct C2;
pub struct C3;
pub struct C4;

pub struct P1;
pub struct P2;
pub struct P3;
pub struct P4;

// pwm_map!(S1, S2, S3, S4);

impl_pins!{C1(P1, C1, true;), C2(;(), false), C3(;(), false)}
impl_pins!{C1(P1, C1, true;), C2(;(), false), C3(P3, C3, true;)}