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<h2 align="center">The newtype with guarantees.</h2>

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Nutype is a proc macro that allows adding extra constraints like _sanitization_ and _validation_ to the regular [newtype pattern](https://doc.rust-lang.org/rust-by-example/generics/new_types.html). The generated code makes it impossible to instantiate a value without passing the checks. It works this way even with `serde` deserialization.


* [Quick start](#quick-start)
* [Inner types](#inner-types) ([String](#string) | [Integer](#integer) | [Float](#float) | [Other](#other-inner-types-and-generics))
* [Custom](#custom-sanitizers) ([sanitizers](#custom-sanitizers) | [validators](#custom-validators) | [errors](#custom-validation-with-a-custom-error-type))
* [Deriving traits](#deriving-traits)
* [Constants](#constants)
* [Recipes](#recipes)
* [Constructor visibility](#constructor-visibility)
* [Breaking constraints with new_unchecked](#breaking-constraints-with-new_unchecked)
* [Feature Flags](#feature-flags)
* [Support Ukrainian military forces](#support-ukrainian-military-forces)
* [Similar projects](#similar-projects)

## Quick start

```rust
use nutype::nutype;

// Define newtype Username
#[nutype(
    sanitize(trim, lowercase),
    validate(not_empty, len_char_max = 20),
    derive(Debug, PartialEq, Clone),
)]
pub struct Username(String);

// We can obtain a value of Username with `::try_new()`.
// Note that Username holds a sanitized string
assert_eq!(
    Username::try_new("   FooBar  ").unwrap().into_inner(),
    "foobar"
);

// It's impossible to obtain an invalid Username
// Note that we also got `UsernameError` enum generated implicitly
// based on the validation rules.
assert_eq!(
    Username::try_new("   "),
    Err(UsernameError::NotEmptyViolated),
);
assert_eq!(
    Username::try_new("TheUserNameIsVeryVeryLong"),
    Err(UsernameError::LenCharMaxViolated),
);
```

For more please see:
* [Examples](https://github.com/greyblake/nutype/tree/master/examples)
* [Tests](https://github.com/greyblake/nutype/tree/master/test_suite/tests)


## Inner types

Available sanitizers, validators, and derivable traits are determined by the inner type, which falls into the following categories:
* String
* Integer (`u8`, `u16`,`u32`, `u64`, `u128`, `i8`, `i16`, `i32`, `i64`, `i128`, `usize`, `isize`)
* Float (`f32`, `f64`)
* Anything else

## String

At the moment the string inner type supports only `String` (owned) type.

### String sanitizers

| Sanitizer   | Description                                                                         | Example                                         |
|-------------|-------------------------------------------------------------------------------------|-------------------------------------------------|
| `trim`      | Removes leading and trailing whitespaces                                            | `trim`                                          |
| `lowercase` | Converts the string to lowercase                                                    | `lowercase`                                     |
| `uppercase` | Converts the string to uppercase                                                    | `uppercase`                                     |
| `with`      | Custom sanitizer. A function or closure that receives `String` and returns `String` | `with = \|mut s: String\| ( s.truncate(5); s )` |

### String validators

| Validator       | Description                                                                     | Error variant         | Example                                      |
|-----------------|---------------------------------------------------------------------------------|-----------------------|----------------------------------------------|
| `len_char_min`  | Min length of the string (in chars, not bytes)                                  | `LenCharMinViolated`  | `len_char_min = 5`                           |
| `len_char_max`  | Max length of the string (in chars, not bytes)                                  | `LenCharMaxViolated`  | `len_char_max = 255`                         |
| `len_utf16_min` | Min length of the string in UTF-16 code units (useful for JavaScript interop)   | `LenUtf16MinViolated` | `len_utf16_min = 5`                          |
| `len_utf16_max` | Max length of the string in UTF-16 code units (useful for JavaScript interop)   | `LenUtf16MaxViolated` | `len_utf16_max = 255`                        |
| `not_empty`     | Rejects an empty string                                                         | `NotEmptyViolated`    | `not_empty`                                  |
| `regex`         | Validates format with a regex. Requires `regex` feature.                        | `RegexViolated`       | `regex = "^[0-9]{7}$"` or `regex = ID_REGEX` |
| `predicate`     | Custom validator. A function or closure that receives `&str` and returns `bool` | `PredicateViolated`   | `predicate = \|s: &str\| s.contains('@')`    |
| `with`          | Custom validator with a custom error                                            | N/A                   | (see example below)                          |


#### Regex validation

Requirements:
* `regex` feature of `nutype` is enabled.
* You have to explicitly include `regex` as a dependency.

There are a number of ways you can use regex.

A regular expression can be defined right in place:

```rs
#[nutype(validate(regex = "^[0-9]{3}-[0-9]{3}$"))]
pub struct PhoneNumber(String);
```

or it can be defined with `std::sync::LazyLock`:

```rs
use regex::Regex;

static PHONE_NUMBER_REGEX: LazyLock<Regex> = LazyLock::new(|| Regex::new("^[0-9]{3}-[0-9]{3}$").unwrap());

#[nutype(validate(regex = PHONE_NUMBER_REGEX))]
pub struct PhoneNumber(String);
```

or it can be defined with `lazy_static`:

```rs
use lazy_static::lazy_static;
use regex::Regex;

lazy_static! {
    static ref PHONE_NUMBER_REGEX: Regex = Regex::new("^[0-9]{3}-[0-9]{3}$").unwrap();
}

#[nutype(validate(regex = PHONE_NUMBER_REGEX))]
pub struct PhoneNumber(String);
```

or `once_cell`:

```rs
use once_cell::sync::Lazy;
use regex::Regex;

static PHONE_NUMBER_REGEX: Lazy<Regex> =
    Lazy::new(|| Regex::new("[0-9]{3}-[0-9]{3}$").unwrap());

#[nutype(validate(regex = PHONE_NUMBER_REGEX))]
pub struct PhoneNumber(String);
```


### String derivable traits

The following traits can be derived for a string-based type:
`Debug`, `Clone`, `PartialEq`, `Eq`, `PartialOrd`, `Ord`, `FromStr`, `AsRef`, `Deref`,
`From`, `TryFrom`, `Into`, `Hash`, `Borrow`, `Display`, `Default`, `Serialize`, `Deserialize`.


## Integer

The integer inner types are: `u8`, `u16`,`u32`, `u64`, `u128`, `i8`, `i16`, `i32`, `i64`, `i128`, `usize`, `isize`.

### Integer sanitizers

| Sanitizer | Description       | Example                            |
|-----------|-------------------|------------------------------------|
| `with`    | Custom sanitizer. | `with = \|raw\| raw.clamp(0, 100)` |

### Integer validators

| Validator           | Description                           | Error variant             | Example                              |
| ------------------- | ------------------------------------- | ------------------------- | ------------------------------------ |
| `less`              | Exclusive upper bound                 | `LessViolated`            | `less = 100`                         |
| `less_or_equal`     | Inclusive upper bound                 | `LessOrEqualViolated`     | `less_or_equal = 99`                 |
| `greater`           | Exclusive lower bound                 | `GreaterViolated`         | `greater = 17`                       |
| `greater_or_equal`  | Inclusive lower bound                 | `GreaterOrEqualViolated`  | `greater_or_equal = 18`              |
| `predicate`         | Custom predicate                      | `PredicateViolated`       | `predicate = \|num\| num % 2 == 0`   |
| `with`              | Custom validator with a custom error  | N/A                       | (see example below)                  |

### Integer derivable traits

The following traits can be derived for an integer-based type:
`Debug`, `Clone`, `Copy`, `PartialEq`, `Eq`, `PartialOrd`, `Ord`, `FromStr`, `AsRef`, `Deref`,
`Into`, `From`, `TryFrom`, `Hash`, `Borrow`, `Display`, `Default`, `Serialize`, `Deserialize`.


## Float

The float inner types are: `f32`, `f64`.

### Float sanitizers

| Sanitizer | Description       | Example                                |
|-----------|-------------------|----------------------------------------|
| `with`    | Custom sanitizer. | `with = \|val\| val.clamp(0.0, 100.0)` |

### Float validators

| Validator          | Description                          | Error variant            | Example                             |
| ------------------ | ------------------------------------ | ------------------------ | ----------------------------------- |
| `less`             | Exclusive upper bound                | `LessViolated`           | `less = 100.0`                      |
| `less_or_equal`    | Inclusive upper bound                | `LessOrEqualViolated`    | `less_or_equal = 100.0`             |
| `greater`          | Exclusive lower bound                | `GreaterViolated`        | `greater = 0.0`                     |
| `greater_or_equal` | Inclusive lower bound                | `GreaterOrEqualViolated` | `greater_or_equal = 0.0`            |
| `finite`           | Check against NaN and infinity       | `FiniteViolated`         | `finite`                            |
| `predicate`        | Custom predicate                     | `PredicateViolated`      | `predicate = \|val\| val != 50.0`   |
| `with`             | Custom validator with a custom error | N/A                      | (see example below)                 |

### Float derivable traits

The following traits can be derived for a float-based type:
`Debug`, `Clone`, `Copy`, `PartialEq`, `Eq`, `PartialOrd`, `Ord`, `FromStr`, `AsRef`, `Deref`,
`Into`, `From`, `TryFrom`, `Hash`, `Borrow`, `Display`, `Default`, `Serialize`, `Deserialize`.

It's also possible to derive `Eq` and `Ord` if the validation rules guarantee that `NaN` is excluded.
This can be done applying by `finite` validation. For example:

```rust
#[nutype(
    validate(finite),
    derive(PartialEq, Eq, PartialOrd, Ord),
)]
struct Size(f64);
```

## Other inner types and generics

For any other type it is possible to define custom sanitizers with `with` and custom
validations with `predicate`:

```rust
use nutype::nutype;

#[nutype(
    derive(Debug, PartialEq, AsRef, Deref),
    sanitize(with = |mut guests| { guests.sort(); guests }),
    validate(predicate = |guests| !guests.is_empty() ),
)]
pub struct GuestList(Vec<String>);
```

It's also possible to use generics:

```rust
#[nutype(
    sanitize(with = |mut v| { v.sort(); v }),
    validate(predicate = |vec| !vec.is_empty()),
    derive(Debug, PartialEq, AsRef, Deref),
)]
struct SortedNotEmptyVec<T: Ord>(Vec<T>);

let wise_friends = SortedNotEmptyVec::try_new(vec!["Seneca", "Zeno", "Plato"]).unwrap();
assert_eq!(wise_friends.as_ref(), &["Plato", "Seneca", "Zeno"]);
assert_eq!(wise_friends.len(), 3);

let numbers = SortedNotEmptyVec::try_new(vec![4, 2, 7, 1]).unwrap();
assert_eq!(numbers.as_ref(), &[1, 2, 4, 7]);
assert_eq!(numbers.len(), 4);
```

### Where clauses

Nutype fully supports `where` clauses in generic newtypes, including Higher-Ranked Trait Bounds (HRTB):

```rust
use nutype::nutype;

// Simple where clause
#[nutype(derive(Debug, Clone))]
struct Wrapper<T>(T)
where
    T: Default + Clone;

// HRTB for collections - validate that collection is non-empty
#[nutype(
    validate(predicate = |c| c.into_iter().next().is_some()),
    derive(Debug)
)]
struct NonEmpty<C>(C)
where
    for<'a> &'a C: IntoIterator;

// Usage
let non_empty = NonEmpty::try_new(vec![1, 2, 3]).unwrap();
assert!(NonEmpty::try_new(Vec::<i32>::new()).is_err());
```

## Custom sanitizers

You can set custom sanitizers using the `with` option.
A custom sanitizer is a function or closure that receives a value of an inner type with ownership and returns a sanitized value.

For example, this one

```rust
#[nutype(sanitize(with = new_to_old))]
pub struct CityName(String);

fn new_to_old(s: String) -> String {
    s.replace("New", "Old")
}
```

is equal to the following one:

```rust
#[nutype(sanitize(with = |s| s.replace("New", "Old") ))]
pub struct CityName(String);
```

And works the same way:

```rust
let city = CityName::new("New York");
assert_eq!(city.into_inner(), "Old York");
```

## Custom validators

In similar fashion it's possible to define custom validators, but a validation function receives a reference and returns `bool`.
Think of it as a predicate.

```rust
#[nutype(validate(predicate = is_valid_name))]
pub struct Name(String);

fn is_valid_name(name: &str) -> bool {
    // A fancy way to verify if the first character is uppercase
    name.chars().next().map(char::is_uppercase).unwrap_or(false)
}
```

## Custom validation with a custom error type

To define your own error type and implement custom validation logic, you can combine the `with` and `error` attributes:

```rust
// Define a custom error type for validation failures.
// Although it's best practice to implement `std::error::Error` for custom error types,
// we are omitting that for simplicity here.
#[derive(Debug, PartialEq)]
enum NameError {
    TooShort,
    TooLong,
}

// Define a custom validation function for `Name`.
// The function returns `Result<(), NameError>`, where `Ok(())` indicates a valid name,
// and `Err(NameError)` represents a specific validation failure.
fn validate_name(name: &str) -> Result<(), NameError> {
    if name.len() < 3 {
        Err(NameError::TooShort)
    } else if name.len() > 10 {
        Err(NameError::TooLong)
    } else {
        Ok(())
    }
}

// Define a newtype `Name` with custom validation logic and custom error.
#[nutype(
    validate(with = validate_name, error = NameError),
    derive(Debug, PartialEq),
)]
struct Name(String);
```

It's important to ensure that the type specified in the `error` attribute matches the error type returned by the validation function.


## Deriving Traits

There are two ways to derive traits for a `nutype`.

### `derive`

The recommended approach is to use the `derive(..)` attribute within the `#[nutype(..)]` macro:

```rust
#[nutype(derive(Debug))]
pub struct Username(String);
```

When using `derive`, `nutype` ensures that the derived traits do not compromise the type's invariants (i.e., validation constraints).

However, this approach has a limitation: only a predefined set of traits is supported. Deriving arbitrary third-party traits is not allowed via `derive`.

### `derive_unchecked`

To overcome this limitation, you can use the `derive_unchecked(..)` attribute (requires the corresponding feature flag to be enabled):

```rust
use derive_more::DerefMut;

#[nutype(derive_unchecked(DerefMut))]
pub struct Username(String);
```

This enables deriving arbitrary traits, including those from third-party crates.
However, **use this with caution**: `nutype` cannot verify that these traits preserve the invariants of the type.
It is the developer's responsibility to ensure that the derived traits do not introduce ways to bypass validation (e.g., by allowing mutable access to the inner value).


### `cfg_attr`

You can use `cfg_attr` to conditionally derive traits based on `cfg` predicates:

```rust
#[nutype(
    derive(Debug, PartialEq),
    cfg_attr(feature = "serde", derive(Serialize, Deserialize)),
)]
pub struct Email(String);
```

Only `derive(...)` and `derive_unchecked(...)` are supported inside `cfg_attr`.

Complex predicates work as well:

```rust
#[nutype(
    derive(Debug),
    cfg_attr(all(test, debug_assertions), derive(Clone, Display)),
)]
pub struct Label(String);
```

Multiple `cfg_attr` entries are allowed:

```rust
#[nutype(
    derive(Debug),
    cfg_attr(test, derive(Clone)),
    cfg_attr(feature = "serde", derive(Serialize, Deserialize)),
)]
pub struct Tag(String);
```

Note that a trait cannot appear in both unconditional `derive` and `cfg_attr` `derive` at the same time.


## Constants

You can mark a type with the `const_fn` flag. In that case, its `new` and `try_new` functions will be declared as `const`:

```rust
#[nutype(
    const_fn,
    derive(Debug),
    validate(greater_or_equal = -273.15),
)]
pub struct Celsius(f64);
```

Since `Result::unwrap()` is not allowed in `const` contexts, we must manually handle the `Result` when creating constants. Any attempt to instantiate an invalid `Celsius` at compile time will trigger a compilation error:

```rust
const FREEZING_POINT: Celsius = match Celsius::try_new(0.0) {
    Ok(value) => value,
    Err(_) => panic!("Invalid value"),
};
```

Alternatively, you can use a helper macro like this:

```rust
macro_rules! nutype_const {
    ($name:ident, $ty:ty, $value:expr) => {
        const $name: $ty = match <$ty>::try_new($value) {
            Ok(value) => value,
            Err(_) => panic!("Invalid value"),
        };
    };
}

nutype_const!(WATER_BOILING_POINT, Celsius, 100.0);
```

Note that `const` works only for stack allocated types.
If you are dealing with a heap allocated type (e.g. `String`) you should consider using `static` with [`LazyLock`](https://doc.rust-lang.org/beta/std/sync/struct.LazyLock.html).

## Recipes

### Obtaining a reference to the inner value

The function `.into_inner()` takes ownership of the newtype and returns its inner type. However, if you only need to borrow the inner value (rather than consume it), you can derive `AsRef`. This allows you to call `as_ref()` to obtain a reference to the underlying data:

```rs
#[nutype(derive(AsRef))]
struct Username(String);

let username = Username::new("Jack");
assert_eq!(username.as_ref(), "Jack");
```

### Derive `Default`

```rs
#[nutype(
    derive(Default),
    default = "Anonymous",
)]
pub struct Name(String);
```

### Derive `Eq` and `Ord` on float types

With nutype it's possible to derive `Eq` and `Ord` if there is `finite` validation set.
The `finite` validation ensures that the valid value excludes `NaN`.

```rs
#[nutype(
    validate(finite),
    derive(PartialEq, Eq, PartialOrd, Ord),
)]
pub struct Weight(f64);
```


## Constructor visibility

By default, the constructor functions (`new()` or `try_new()`) are public. You can control their visibility using the `constructor(visibility = ...)` attribute:

```rust
// Private constructor - only accessible within the defining module
#[nutype(
    sanitize(trim),
    constructor(visibility = private),
)]
pub struct InternalName(String);

// Crate-level visibility
#[nutype(
    validate(not_empty),
    constructor(visibility = pub(crate)),
)]
pub struct CrateName(String);
```

Available visibility options:
- `private` - Only accessible within the defining module
- `pub(crate)` - Accessible within the current crate
- `pub` - Public (default behavior)

This is useful when you want to restrict where instances can be created, ensuring they only come from trusted factory functions or specific modules.

## Breaking constraints with new_unchecked

It's discouraged, but it's possible to bypass the constraints by enabling `new_unchecked` crate feature and marking a type with `new_unchecked`:

```rs
#[nutype(
    new_unchecked,
    sanitize(trim),
    validate(len_char_min = 8)
)]
pub struct Name(String);

// Yes, you're forced to use `unsafe` here, so everyone will point fingers at YOU.
let name = unsafe { Name::new_unchecked(" boo ".to_string()) };

// `name` violates the sanitization and validation rules!!!
assert_eq!(name.into_inner(), " boo ");
```

## Feature flags

* `arbitrary` - enables derive of [`arbitrary::Arbitrary`](https://docs.rs/arbitrary/latest/arbitrary/trait.Arbitrary.html).
* `derive_unchecked` - enables `derive_unchecked` attribute to derive any arbitrary trait.
* `new_unchecked` - enables generation of unsafe `::new_unchecked()` function.
* `regex` - allows to use `regex = ` validation on string-based types. Note: your crate also has to explicitly have `regex` within its dependencies.
* `serde` - integrations with [`serde`](https://crates.io/crates/serde) crate. Allows to derive `Serialize` and `Deserialize` traits.
* `schemars08` - allows to derive [`JsonSchema`](https://docs.rs/schemars/0.8.12/schemars/trait.JsonSchema.html) trait of [schemars](https://crates.io/crates/schemars) crate. Note that at the moment validation rules are not respected.
* `std` - enabled by default. Use `default-features = false` to disable.

## When nutype is a good fit for you?

* If you enjoy [newtype](https://doc.rust-lang.org/book/ch19-04-advanced-types.html#using-the-newtype-pattern-for-type-safety-and-abstraction)
  pattern and you like the idea of leveraging the Rust type system to enforce the correctness of the business logic.
* If you want to use type system to hold invariants
* If you're a DDD fan, nutype is a great helper to make your domain models even more expressive.
* You want to prototype quickly without sacrificing quality.

## When nutype is not that good?

* You care too much about compiler time (nutype relies on heavy usage of proc macros).
* You think metaprogramming is too much implicit magic.
* IDEs may not be very helpful at giving you hints about proc macros.
* Design of nutype may enforce you to run unnecessary validation (e.g. on loading data from DB), which may have a negative impact if you aim for extreme performance.

## Support Ukrainian military forces

Today I live in Berlin, I have the luxury to live a physically safe life.
But I am Ukrainian. The first 25 years of my life I spent in [Kharkiv](https://en.wikipedia.org/wiki/Kharkiv),
the second-largest city in Ukraine, 60km away from the border with russia. Today about [a third of my home city is destroyed](https://www.youtube.com/watch?v=ihoufBFSZds) by russians.
My parents, my relatives and my friends had to survive the artillery and air attack, living for over a month in basements.

Some of them have managed to evacuate to EU. Some others are trying to live "normal lives" in Kharkiv, doing there daily duties.
And some are at the front line right now, risking their lives every second to protect the rest.

I encourage you to donate to [Charity foundation of Serhiy Prytula](https://prytulafoundation.org/en).
Just pick the project you like and donate. This is one of the best-known foundations, you can watch a [little documentary](https://www.youtube.com/watch?v=VlmWqoeub1Q) about it.
Your contribution to the Ukrainian military force is a contribution to my calmness, so I can spend more time developing the project.

Thank you.

## Similar projects

* [prae](https://github.com/teenjuna/prae) - A very similar crate that aims to solve the same problems but with slightly different approach.
* [bounded-integer](https://github.com/Kestrer/bounded-integer) - Bounded integers for Rust.
* [refinement](https://docs.rs/refinement/latest/refinement/) - Convenient creation of type-safe refinement types (based on generics).
* [semval](https://github.com/slowtec/semval) - Semantic validation for Rust.
* [validator](https://github.com/Keats/validator) - Simple validation for Rust structs (powered by macros).
* [derive_more](https://github.com/JelteF/derive_more) - If you just need to derive traits on a newtype without extra logic.

## License

MIT © [Serhii Potapov](https://www.greyblake.com)
