Macro _params 

macro_rules! _params {
    () => { ... };
    ($name:ident = $value:expr) => { ... };
    ($value:expr) => { ... };
    ($($name:ident = $value:expr),*) => { ... };
    (@acc [$($acc:tt)*];) => { ... };
    (@acc [$($acc:tt)*]; $name:ident = $value:expr) => { ... };
    (@acc [$($acc:tt)*]; $value:expr) => { ... };
    (@acc [$($acc:tt)*]; $name:ident = $value:expr, $($tail:tt)*) => { ... };
    (@acc [$($acc:tt)*]; $value:expr, $($tail:tt)*) => { ... };
    ($name:ident = $value:expr, $($tail:tt)*) => { ... };
    ($value:expr, $($tail:tt)*) => { ... };
}

Creates a vector of formatting parameters.

This macro takes a comma-separated list of expressions and converts each into a Parameter. Each expression is processed by the param! macro.