Build

The Build derive macro generates a type-safe fluent builder for your struct. Annotate fields with #[moxy(build)] to include them in the builder, then call YourStruct::new() to get a builder instance.

The builder uses const generic bools to track which required fields have been set. Missing a required field is a compile error — not a runtime panic. Setters can be called in any order, and setting a required field twice is also a compile error.

Basic Usage

use moxy::Build;

#[derive(Build, Default)]
struct Config {
    #[moxy(build)]
    pub host: String,
    #[moxy(build)]
    pub port: u16,
}

let config = Config::new()
    .host("localhost")
    .port(8080_u16)
    .build();

assert_eq!(config.host, "localhost");
assert_eq!(config.port, 8080);

Build generates:

• A ConfigBuilder struct with const generic bools tracking required field state
• A setter method per annotated field that accepts V: Into<T> for flexible conversions
• A build() method — only available once all required fields are set
• A Config::new() factory that returns a fresh ConfigBuilder

Non-annotated fields are initialised with Default::default() via a struct spread.

Note

Build requires the struct to also implement Default — either #[derive(Default)] or a manual impl Default. This is needed to initialise unannotated fields via the struct spread in build().

What’s Next

• Setters — V: Into<T> setter pattern, partial annotation, required vs optional fields
• Defaults — inline fallback values with default = <expr>
• Custom Names — override the generated setter method name
• Generics — using Build with generic structs