Macro trace

macro_rules! trace {
    (target: $target:expr, { $( $($k:ident).+ = $val:expr ),*, }, $($arg:tt)+ ) => { ... };
    (target: $target:expr, { $( $($k:ident).+ = $val:expr ),* }, $($arg:tt)+ ) => { ... };
    (target: $target:expr, $( $($k:ident).+ = $val:expr ),*, ) => { ... };
    (target: $target:expr, $( $($k:ident).+ = $val:expr ),* ) => { ... };
    (target: $target:expr, $($arg:tt)+ ) => { ... };
    ({ $( $($k:ident).+ = $val:expr ),*, }, $($arg:tt)+ ) => { ... };
    ({ $( $($k:ident).+ = $val:expr ),* }, $($arg:tt)+ ) => { ... };
    ($( $($k:ident).+ = $val:expr ),*, ) => { ... };
    ($( $($k:ident).+ = $val:expr ),* ) => { ... };
    ($($arg:tt)+ ) => { ... };
}

Constructs an event at the trace level.

When both a message and fields are included, curly braces ({ and }) are used to delimit the list of fields from the format string for the message. A trailing comma on the final field is valid.

Examples

use tokio_trace::field;

let pos = Position { x: 3.234, y: -1.223 };
let origin_dist = pos.dist(Position::ORIGIN);

trace!(position = field::debug(pos), origin_dist = field::debug(origin_dist));
trace!(target: "app_events",
        { position = field::debug(pos) },
        "x is {} and y is {}",
       if pos.x >= 0.0 { "positive" } else { "negative" },
       if pos.y >= 0.0 { "positive" } else { "negative" });