derive-adhoc: An ergonomic replacement for (some) proc macros

derive-adhoc allows you to write macros which are driven by Rust data structures, just like proc macro derive macros, but without having to wrestle with the proc macro system.

Stability warning

We plan to make a 1.x version of this library fairly soon.

However, it will have a different name: derive-deftly. If you are considering this for a new project, you should probably go straight to derive-deftly.

Some further breaking changes are expected for that library, so if you're already using derive-adhoc you should stick with it for now.

The template syntax isn't likely to change very much.

Overview

You can write an ad-hoc template, which can speak about the fields and types in the data structure. You can also define named templates and apply them to multiple structures: effectively, you can define your own derive macro.

You don't need to make a separate proc macro crate, write to the syn and proc_macro APIs. take care to properly propagate compile errors, or, generally, do any of the things that make writing proc macros so complicated.

The template language resembles the "expander" part of a macro_rules macro, but you don't have to write the "matcher" part: derive-adhoc parses the input data structure for you, and makes the pieces available via predefined expansion variables.

Further documentation is available in the doc_ module(s) and the docs for the individual proc macros.

Simple example - providing Vec containing enum variant names

use derive_adhoc::{define_derive_adhoc, Adhoc};

define_derive_adhoc! {
    ListVariants =

    impl $ttype {
        fn list_variants() -> Vec<&'static str> {
            vec![ $( stringify!( $vname ) , ) ]
        }
    }
}

#[derive(Adhoc)]
#[derive_adhoc(ListVariants)]
enum Enum {
    UnitVariant,
    StructVariant { a: u8, b: u16 },
    TupleVariant(u8, u16),
}

assert_eq!(
    Enum::list_variants(),
    ["UnitVariant", "StructVariant", "TupleVariant"],
);

Next steps

Why not have a look at our friendly introduction?

It will walk you through derive-adhoc's most important features, with a number of worked examples,