Crate mux_attrs 

Attribute multiplexing.

Here this means repeating original code multiple times but with different attributes.

Examples

Different default enum variants

use mux_attrs::{From, Mux};

#[derive(Mux)]
#[mux_names(b = B, c = C)]
#[derive(Clone, Copy, From, PartialEq, Eq, Debug)]
#[from(A, B, C)]
#[mux(derive(Default))]
enum A {
    #[mux(b = default)]
    X,
    #[mux(c = default)]
    Y,
}

In this example B::default() returns B::X, C::default() returns C::Y, while A hasn’t default constructor at all. Also all these enums can be converted to each other via from or into.

Different struct binary representation

use mux_attrs::{From, Mux};

#[derive(Mux)]
#[mux_names(b = B, c = C)]
#[derive(Clone, Copy, From, PartialEq, Eq, Debug)]
#[from(A, B, C)]
#[mux(b = repr(C),c = repr(C, packed))]
struct A(u8, u32);

assert_eq!((size_of::<B>(), align_of::<B>()), (8, 4));
assert_eq!((size_of::<C>(), align_of::<C>()), (5, 1));

Derive macros

Mux

Derive macro that actually performs multiplexing.

It simply repeats the item declaration multiple times except:

• Original #[derive(Mux, ...)] attribute, but not subsequent.
• The name of original item - it is replaced by names from mux_names.
• #[mux_names(...)] attribute.
• #[mux(...)] attributes - they are replaced by their content depending on keys.

#[mux_names(...)] attribute specifies names of repeated item.

There are two forms:

• #[mux_names(TypeName1)] for single repetition only,
• #[mux_names(key1 = TypeName1, key2 = TypeName2, ...)] for multiple repetitions.

#[mux(...)] attributes specifies attributes to substitute in repeated item. The general form is #[mux(default_attribute, key1 = attribute_for_item1, key2 = attribute_for_item2, ...)], where keys are taken from mux_names macro. If there’s no both default_attribte and current repetiton key, then the attribute is simply skipped.

From

Helper derive macro that implements casting between different types with the same fields or variants.

Requires attribute of form #[from(A, B, C)], where A, B and C are types should be converted from. If one of the types is the same as the name of the item itself then it is ignored.

Derive Macros

From

Mux