Macro alloc 

macro_rules! alloc {
    () => { ... };
    (if { $($p:tt)* } else { $($n:tt)* }) => { ... };
    ($($p:tt)*) => { ... };
}

Indicates the alloc crate is available and can be used.

This macro passes the provided code because #[cfg(feature = "alloc")] is currently active.