format-attr

document: https://docs.rs/format-attr

A Rust proc-macro crate that provides custom derive macros for implementing Display and Debug traits with custom format strings.

Features

• DisplayAttr - Derive std::fmt::Display with a custom format string
• DebugAttr - Derive std::fmt::Debug with a custom format string
• DisplayAsDebug - Implement Display by delegating to the existing Debug implementation
• Support for separate format strings via #[fmt_display(...)] and #[fmt_debug(...)]
• Fallback to shared #[fmt(...)] attribute

Usage

Add this to your Cargo.toml:

[dependencies]
format-attr = "0.1.0"

Basic Example

use format_attr::{DisplayAttr, DebugAttr};

#[derive(DisplayAttr, DebugAttr)]
#[fmt("Point({}, {})", self.x, self.y)]
struct Point {
    x: i32,
    y: i32,
}

let p = Point { x: 10, y: 20 };
assert_eq!(format!("{}", p), "Point(10, 20)");
assert_eq!(format!("{:?}", p), "Point(10, 20)");

Separate Format Strings

Use #[fmt_display(...)] and #[fmt_debug(...)] for different output:

use format_attr::{DisplayAttr, DebugAttr};

#[derive(DisplayAttr, DebugAttr)]
#[fmt_display("User: {}", self.name)]
#[fmt_debug("User {{ name: {}, age: {} }}", self.name, self.age)]
struct User {
    name: String,
    age: u32,
}

let u = User { name: "Alice".to_string(), age: 30 };
assert_eq!(format!("{}", u), "User: Alice");
assert_eq!(format!("{:?}", u), "User { name: Alice, age: 30 }");

DisplayAsDebug

When you want Display to use the same output as Debug:

use format_attr::DisplayAsDebug;

#[derive(Debug, DisplayAsDebug)]
struct Value(i32);

let v = Value(42);
assert_eq!(format!("{}", v), "Value(42)");
assert_eq!(format!("{:?}", v), "Value(42)");

Attribute Priority

License

MIT