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

• no_std compatible: Works in no_std environments with optional alloc support for String types.

• Derive trait StrongType: Create a named strong type.

  • The macro automatically implements Clone, Debug, PartialEq, and PartialOrd, and will conditionally add Copy, Default, Eq, Ord, and Hash when appropriate. Send and Sync are automatically derived by Rust when the wrapped type implements them.
  • Every generated type exposes ergonomic helpers such as new, const_new, into_inner, as_ref, and as_mut, plus blanket AsRef/AsMut implementations so you can seamlessly borrow the inner value.
  • 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 with all ownership variants (owned, &Self, etc.).
      • Use auto_operators = "delegated" when you want all ownership combinations but prefer smaller binaries (requires the primitive type to be Copy); delegated mode routes operator bodies through shared helpers in strong_type::delegation, trimming monomorphization in debug builds at the cost of a small inlining opportunity.
      • Use auto_operators = "minimal" for a lightweight version that generates only owned-value operations, reducing binary size while maintaining core functionality.
      • Use auto_operators = "full" or just auto_operators for the complete set of operator implementations.
    • 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/Into for owned and borrowed variants of the underlying type, making it easy to cross the boundary when needed. 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 = "1.1"

no_std Support

This crate supports no_std environments. By default, the std feature is enabled.

# Default (with std)
strong-type = "1.1"

# no_std with alloc (for String support)
strong-type = { version = "1.1", default-features = false, features = ["alloc"] }

# no_std without alloc (primitives only)
strong-type = { version = "1.1", default-features = false }

Note: std and alloc are functionally equivalent for this crate. The std feature (enabled by default) exists for convention and future compatibility.

When using String in no_std mode, import it from the crate:

use strong_type::{StrongType, String};

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

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));

Minimal operators for reduced binary size:

use strong_type::StrongType;

// Full mode: generates operators for all ownership combinations
// (Type + Type, Type + &Type, &Type + Type, &Type + &Type)
#[derive(StrongType)]
#[strong_type(auto_operators)]  // or auto_operators = "full"
struct FullPrice(i32);

let x = FullPrice::new(10);
let y = FullPrice::new(20);
assert_eq!(&x + &y, FullPrice(30));  // Works with references

// Minimal mode: generates only owned operations for smaller binary size
#[derive(StrongType)]
#[strong_type(auto_operators = "minimal")]
struct MinimalPrice(i32);

let x = MinimalPrice::new(10);
let y = MinimalPrice::new(20);
assert_eq!(x + y, MinimalPrice(30));  // Works with owned values
// assert_eq!(&x + &y, MinimalPrice(30));  // Won't compile - references not supported

// Minimal mode still supports:
// - All basic operators: +, -, *, /, %
// - Assignment operators: +=, -=, *=, /=, %=
// - Negation: -x
// - Iterator traits: Sum, Product

Delegated operators for shared codegen

use strong_type::StrongType;

#[derive(StrongType)]
#[strong_type(auto_operators = "delegated")]
struct DelegatedPrice(i32);

let x = DelegatedPrice::new(10);
let y = DelegatedPrice::new(20);
assert_eq!(&x + &y, DelegatedPrice(30)); // All ownership variants still compile

Delegated mode emits the full operator surface but forwards every body to small helpers in strong_type::delegation. This keeps ergonomics identical to auto_operators = "full" while trimming monomorphization-heavy code, typically shrinking debug binaries by 30-50% versus the full mode. Because those helpers are marked #[inline(never)], expect a tiny throughput regression when micro-benchmarked (<2% in our perf examples), which is usually offset by faster builds and smaller artifacts.

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.