just_template

a tool for code gen via templates

Template File Writing Rules

just_template gens repetitive code using three core concepts: impl_mark, impl_area, and param.

1. impl_mark Mark an "impl point" with a line starting with 10 > chars: >>>>>>>>>> NAME. Used for positioning. The system extracts the matching impl_area content and expands it here.

2. impl_area Declare a reusable code template: @@@ NAME >>> [template content] @@@ <<< Inside, use param placeholders like <<<PARAM>>>. When adding an impl via cmd (e.g., insert_impl!), the system copies the area, replaces params, and appends to the impl_mark.

3. param

   • Params outside an impl_area are replaced globally.
   • Params inside are replaced per-impl when generating.

Example:

Template:

// Auto generated
use std::collections::HashMap;

pub async fn my_func(
    name: &str,
    data: &[u8],
    params: &HashMap<String, String>,
) -> Option<Result<Vec<u32>, std::io::Error>> {
    match name {
>>>>>>>>>> arms
@@@ >>> arms
        "<<<crate_name>>>" => Some(<<<crate_name>>>::exec(data, params).await),
@@@ <<<
        _ => None,
    }
}

Run cmds:

tmpl!(tmpl += {
    arms {
        (crate_name = "my"),
        (crate_name = "you")
    }
});

The arms impl_area becomes:

        "my" => Some(my::exec(data, params).await),
        "you" => Some(you::exec(data, params).await),

Final expanded code:

// Auto generated
use std::collections::HashMap;

pub async fn my_func(
    name: &str,
    data: &[u8],
    params: &HashMap<String, String>,
) -> Option<Result<Vec<u32>, std::io::Error>> {
    match name {
        "my" => Some(my::exec(data, params).await),
        "you" => Some(you::exec(data, params).await),
        _ => None,
    }
}

Installation

Add this to your Cargo.toml:

[dependencies]
just_template = "0.1"

License

This project is dual-licensed under MIT and Apache 2.0. See the LICENSE file for details.