# Virtue, a sinless derive macro helper

## Goals

- Zero dependencies, so fast compile times
- No other dependencies needed
- Declarative code generation
- As much typesystem checking as possible
- Build for modern rust: 1.57 and up
- Build with popular crates in mind:
  - [bincode](https://docs.rs/bincode)
- Will always respect semver. Minor releases will never have:
  - Breaking API changes
  - MSRV changes

## Example

```rust
use virtue::prelude::*;

#[proc_macro_derive(YourDerive, attributes(some, attributes, go, here))]
pub fn derive_your_derive(input: TokenStream) -> TokenStream {
    derive_your_derive_inner(input)
        .unwrap_or_else(|error| error.into_token_stream())
}

fn derive_your_derive_inner(input: TokenStream) -> Result<TokenStream> {
    // Parse the struct or enum you want to implement a derive for
    let parse = Parse::new(input)?;
    // Get a reference to the generator
    let (mut generator, body) = parse.into_generator();
    match body {
        Body::Struct(body) => {
            // Implement your struct body here
            // See `Generator` for more information
            generator.impl_for("YourTrait")?
                    .generate_fn("your_fn")
                    .with_self_arg(FnSelfArg::RefSelf)
                    .body(|fn_body| {
                        fn_body.push_parsed("println!(\"Hello world\");");
                    })?;
        },
        Body::Enum(body) => {
            // Implement your enum body here
            // See `Generator` for more information
            generator.impl_for("YourTrait")?
                    .generate_fn("your_fn")
                    .with_self_arg(FnSelfArg::RefSelf)
                    .body(|fn_body| {
                        fn_body.push_parsed("println!(\"Hello world\");");
                    })?;
        },
    }
    generator.finish()
}
```

Will generate

```ignore
impl YourTrait for <Struct or Enum> {
    fn your_fn(&self) { // .generate_fn("your_fn").with_self_arg(FnSelfArg::RefSelf)
        println!("Hello world"); // fn_body.push_parsed(...)
    }
}
```