Macro nanbox::make_nanbox

macro_rules! make_nanbox {
    (
        $(#[$meta:meta])*
        pub unsafe enum $name: ident, $enum_name: ident {
            $($field: ident ($typ: ty)),*
        }
    ) => { ... };
}

Creates an enum which is packed into the signaling NaN representation of f64.

Some limitations apply to make this work in a safe manner.

• The first and only the first variant must hold a f64.
• There must be 8 or fewer variants in the defined enum (this is only checked with debug_assert!)
• Pointers stored in a nanbox must only use the lower 48 bits (checked via debug_assert! only).

#[macro_use]
extern crate nanbox;

// Creates one `nanbox` type called `Value` and one normal enum called `Variant`.
// `From` implementations are generated to converted between these two types as well as `From`
// implementation for each of the types in the match arms (`From<f64>` etc).
make_nanbox!{
    pub unsafe enum Value, Variant {
        Float(f64),
        Byte(u8),
        Int(i32),
        Pointer(*mut Value)
    }
}