strong-type

strong-type is a Rust crate that offers macros to easily create strongly typed and named primitive and string types. Strong typing helps in making code more expressive and less prone to errors, ensuring that each type is used in its intended way.

use strong_type::StrongType;

#[derive(StrongType)]
struct Timestamp(i64);

let timestamp = Timestamp::new(1701620628123456789);
println!("{}", timestamp); // Timestamp(1701620628123456789)

Features

• Derive trait StrongType: Create a named strong type.

  • The macro automatically implement common traits like Clone, Debug, Default, PartialEq, PartialOrd, Send, and Sync. It also implements Display by default, unless overridden by the custom_display attribute.
  • Conditionally, based on the underlying data type, traits like Copy, Eq, Ord, Hash may also be implemented. For primitive data types like i32 or bool, these additional traits will be automatically included.
  • Numeric types, both integer and floating-point, also implement constants MIN, MAX, INFINITY, NEG_INFINITY, and ZERO. Additionally, for floating-point types, NAN is implemented.

• Attributes:

  • Adding the following attributes to #[strong_type(...)] allows for additional features:
    • auto_operators: Automatically implements relevant arithmetic (for numeric types) or logical (for boolean types) operators.
    • addable: Automatically implements the Add, Sub, and other relevant traits. The attribute is a strict subset of auto_operators.
    • scalable: Automatically implements the Mul, Div, Rem, and other relevant traits between a strong typed struct and its primitive type. Note that the attribute is not a subset of auto_operators.
    • custom_display: Allows users to manually implement the Display trait, providing an alternative to the default display format.
    • conversion: Automatically implements From and Into traits for the underlying type. This is optional since conversion may make strong types less distinct.
    • underlying: Specifies the underlying primitive type for nested strong types.

Installation

Add strong-type to your Cargo.toml:

[dependencies]
strong-type = "0.12"

Supported underlying types:

• Integer types: i8, i16, i32, i64, i128, isize
• Unsigned integer types: u8, u16, u32, u64, u128, usize
• Floating-point types: f32, f64
• Boolean type: bool
• char
• String
• Strong types of the above types

Examples

Creating a named strong type:

With a private field:

use strong_type::StrongType;

#[derive(StrongType)]
struct Tag(String);

let tag = Tag::new("dev");
const TAG: Tag = Tag::const_new("prod");

With a public field:

use strong_type::StrongType;

#[derive(StrongType)]
struct Timestamp(pub i64);

let timestamp = Timestamp(1701620628123456789);
println!("{}", timestamp); // Timestamp(1701620628123456789)

Demonstrating type distinctiveness:

use strong_type::StrongType;
use std::any::Any;

#[derive(StrongType)]
struct Second(i32);

#[derive(StrongType)]
struct Minute(i32);

let x = Second::new(2);
let y = Second::new(3);
let z = Minute::new(3);

assert_eq!(x.type_id(), y.type_id()); // Same type: Second
assert_ne!(y.type_id(), z.type_id()); // Different types: Second versus Minute

Utilizing Hashability:

use std::collections::HashSet;

#[derive(StrongType)]
struct Tag(String);

let mut map = HashSet::<Tag>::new();
map.insert(Tag::new("dev"));
map.insert(Tag::new("prod"));
assert_eq!(map.len(), 2);

Named integer type with arithmetic operations:

use strong_type::StrongType;

#[derive(StrongType)]
#[strong_type(auto_operators)]
struct Nanosecond(u32);

let x = Nanosecond::new(2);
let y = Nanosecond::new(3);
let z = Nanosecond::default();

assert_eq!(x.value(), 2);
assert_eq!(y.value(), 3);
assert_eq!(z.value(), 0);
assert!(x < y);
assert!(y >= x);
assert_eq!(x + y, Nanosecond(5));

#[derive(StrongType)]
#[strong_type(scalable)]
struct Millisecond(u32);

let x = Millisecond::new(2);

assert_eq!(x * 3, Millisecond(6));

Named bool type with logical operations:

use strong_type::StrongType;

#[derive(StrongType)]
#[strong_type(auto_operators)]
struct IsTrue(bool);

let x = IsTrue::new(true);
let y = IsTrue::new(false);

assert_eq!(x & y, IsTrue::new(false));
assert_eq!(x | y, IsTrue::new(true));
assert_eq!(x ^ y, IsTrue::new(true));
assert_eq!(!x, IsTrue::new(false));

Custom display implementation with custom_display:

use std::fmt::{Display, Formatter, Result};
use strong_type::StrongType;

#[derive(StrongType)]
#[strong_type(custom_display)]
struct Second(f64);

impl Display for Second {
   fn fmt(&self, f: &mut Formatter) -> Result {
      write!(f, "Second({:.2})", &self.0)
   }
}

println!("{}", Second::new(std::f64::consts::E)); // "Second(2.72)"
println!("{:?}", Second::new(std::f64::consts::E)); // "Second { value: 2.718281828459045 }"

Nested strong types:

#[derive(StrongType)]
#[strong_type(auto_operators)]
struct Dollar(i32);

#[derive(StrongType)]
#[strong_type(auto_operators, underlying = i32)]
struct Cash(Dollar);

#[derive(StrongType)]
#[strong_type(underlying = i32)]
struct Coin(Cash);

Caveats:

• When using #[derive(StrongType)], the traits Eq and PartialEq are implemented with impl. As a result, StructuralEq and StructuralPartialEq remain unimplemented, preventing pattern matching with strong-typed primitives.
• #[strong_type(scalable)] does not work for nested strong types.