Macro linktime 

macro_rules! linktime {
    (
        $(
            $(#[$meta:meta])*
            $vis:vis trait $trait:ident $(: $bound:path $(, $bound2:path)*)? {
                $($item:item)*
            }
        )*
    ) => { ... };
    (
        $(
            $(#[$meta:meta])*
            impl $trait_seg1:ident $(:: $trait_segn:ident)* for $ty:ty {
                $($item:item)*
            }
        )*
    ) => { ... };
}

Available on crate feature linktime only.

Dynamic XSO traits using a link-time registry

This macro is used for (a) declaring DynXso traits using a registry filled at link-time and (b) for registering types with a trait.

Declaring a link-time DynXso trait

To declare a trait as a link-time DynXso trait, wrap its declaration in a linktime! invocation.

Example

use xso::{dynxso::linktime, asxml::AsXmlDyn};

linktime! {
    pub trait MyPayload: AsXmlDyn {}
}

Usage notes

• A bound on Any is automatically added, because it is a requirement for implementing DynXso on dyn Trait.
• If you want to specify more than one trait bound, you have to separate them with , instead of +, due to rustc limitations with declarative macros.
• A trait bound on AsXmlDyn is required (but has to be added manually, as seen in the above example) for Xso<dyn Trait> to implement AsXml.
• This macro automatically calls crate::derive_dyn_traits!, but does not use the default BuilderRegistry, removing the std dependency at the cost of being unable to register more types at runtime.

Implement a DynXso trait

To implement a trait declared with linktime!, wrap the impl block in a linktime! invocation.

Doing so allows a Xso<dyn Trait>’s FromXml implementation to parse the registered type.

Example

use xso::{dynxso::{linktime, Xso}, FromXml, AsXml, asxml::AsXmlDyn, from_bytes};

linktime! {
    trait Foo: AsXmlDyn {}
}

#[derive(FromXml, AsXml, Debug, Clone, Copy)]
#[xml(namespace = "urn:example", name = "a")]
struct A {}

#[derive(FromXml, AsXml, Debug, Clone, Copy)]
#[xml(namespace = "urn:example", name = "b")]
struct B {}

linktime! {
    impl Foo for A {}
    impl Foo for B {}
}

let foo: Xso<dyn Foo> = from_bytes(b"<a xmlns='urn:example'/>").unwrap();
let foo: Xso<dyn Foo> = from_bytes(b"<b xmlns='urn:example'/>").unwrap();

Usage notes

• linktime! can be placed anywhere; unlike the Xso::register_type calls needed with the BuilderRegistry, registrations are handled at compile-time (or more precisely: at link-time, with a minimal startup overhead of postprocessing the list generated by the linker).