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Nestify

Nestify is a Rust library offering a powerful macro to streamline the definition of nested structs and enums. Designed to improve code readability and maintainability

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Abstract

Nestify re-imagines Rust struct and enum definitions with its "Type is Definition" approach, streamlining the way you handle nested structures. Gone are the days of flipping back and forth between type definitions—Nestify Unifies your codebase, making your code cleaner and far more readable.

Nestify is crafted for ease of learning, with its syntax tailored to be comfortable for Rust developers. The aim is for anyone, even those unfamiliar with the Nest macro, to quickly grasp its concept upon first glance.

Features

• Simplify nested struct and enum definitions in Rust.
• Make your codebase more readable and less verbose.
• Ideal for modeling complex API responses.
• Advanced attribute modifiers.
• Works well with Serde.
• Intuitive syntax

Installation

Add this to your Cargo.toml:

[dependencies]
nestify = "0.3.3"

Then use the macro:

use nestify::nest;

[!NOTE] A nightly toolchain might provide better error diagnostics

Quick Examples

Simple Nested Structures

Here's a quick example to show how Nestify simplifies nested struct definitions:

// Define a user profile with nested address and preferences structures
nest! {
    struct UserProfile {
        name: String,
        address: struct Address {
            street: String,
            city: String,
        },
        preferences: struct Preferences {
            newsletter: bool,
        },
    }
}

struct UserProfile {
    name: String,
    address: Address,
    preferences: Preferences,
}

struct Address {
    street: String,
    city: String,
}

struct Preferences {
    newsletter: bool,
}

Simple Nested Enums

// Define a task with a nested status enum
nest! {
    struct Task {
        id: i32,
        description: String,
        status: enum Status {
            Pending,
            InProgress,
            Completed,
        },
    }
}

struct Task {
    id: i32,
    description: String,
    status: Status,
}

enum Status {
    Pending,
    InProgress,
    Completed,
}

Supported definitions

Nestify supports both structs and enums.

// field structs (named)
nest! {
    struct Named {
        f: struct Nested {}
    }
}

// tuple structs (unnamed)
nest! {
    struct Unnamed(struct Nested())
}

// unit structs
nest! {
    struct Unit {
        unit: struct UnitStruct
    }
}


// enums
nest! {
    enum EnumVariants {
        Unit,
        Tuple(i32, struct TupleNested),
        Struct {
            f1: i32,

        }
        DiscriminantVariant = 1,
    }
}
// note: any variant can have a discriminant
// just as in normal rust

// field structs (named)
struct Named {
    f: Nested,
}
struct Nested {}

// tuple structs (unnamed)
struct Unnamed(Nested,);
struct Nested();

// unit structs
struct Unit {
    unit: UnitStruct,
}
struct UnitStruct;


// enums
enum EnumVariants {
    Unit,
    Tuple(i32, TupleNested),
    Struct { 
        f1: i32 
    },
    DiscriminantVariant = 1,
}
struct TupleNested;

Generics

Nestify fully supports Rust's generic parameters. This compatibility ensures that you can incorporate both lifetime and type parameters within your nested struct definitions, just as you would in standard Rust code.

nest! {
    struct Example<'a, T> {
        s: &'a str,
        t: T
    }
}

struct Example<'a, T> { 
    s: &'a str, 
    t: T, 
}

Nested Generics

When defining nested generics, you need to add generics to types. Enter "FishHook" syntax. To define generics on the field use ||<...>. This will let you specify the nested generic types. It also works with lifetimes if needed.

nest! {
    struct Parent<'a> {
        child : struct Child<'c, C> {
            s: &'c str,
            f: C
        } ||<'a, i32>
    }
}

struct Parent<'a> {
    child: Child<'a, i32>,
    //           ^^^^^^^^ FishHook expands to this part
}

struct Child<'c, C> {
    s: &'c str,
    f: C,
}

Attributes

You can apply attributes just like you would with a normal struct.

nest! {
    #[derive(Clone)]
    struct CloneMe {}
}

let x = CloneMe {};
let cl = x.clone();

Recursive Attributes #[meta]*

Using * syntax you can inherit attributes to child structures easily. The attribute will propagate to each nested structure or enum.

nest! {
    #[apply_all]*
    struct One {
        two: struct Two {
            three: struct Three {
                payload: ()
            }
        }
    }
}

#[apply_all]
struct One {
    two: Tow,
}

#[apply_all]
struct Two {
    three: Three,
}

#[apply_all]
struct Three {
    payload: (),
}

Removal Syntax

Disable Propagation #[meta]/

You can end the recursion of an attribute with a / attribute modifier. It will remove a recursive attribute from the current structure and all nested structures

nest! {
    #[nest]*
    struct One {
        two: struct Two {
            three: #[nest]/ 
            struct Three {
                four: struct Four { }
            }
        }
    }
}

#[nest]
struct One {
    two: Two,
}

#[nest]
struct Two {
    three: Three,
}

struct Three {
    four: Four,
}

struct Four {}

Disable Single #[meta]-

Using the - modifier will remove a recursive attribute from a single structure To use the previous example using - instead of /:

nest! {
    #[nest]*
    struct One {
        two: struct Two {
            three: #[nest]- 
            struct Three {
                four: struct Four { }
            }
        }
    }
}

#[nest]
struct One {
    two: Two,
}

#[nest]
struct Two {
    three: Three,
}

struct Three {
    four: Four,
}

#[nest]
struct Four {}

Field Attributes #>[meta]

If you structure has many defined attributes, it can become awkward to define attributes before the nested structure. To combat this, you can define attributes that apply to nested objects before fields and enum variants. This can be accomplished by using #>[meta] syntax. #> will apply the attribute to the next struct.

nest! {
    struct MyStruct {
        #>[derive(Debug)]
        f: struct DebugableStruct { } 
        // equivlent to: 
        // f: #[derive(Debug)]
        // struct DebugableStruct { }
    }
}

struct MyStruct {
    f: DebugableStruct,
}

#[derive(Debug)]
//       ^^^^^ applied to structure and not field `f`
struct DebugableStruct {}

Enum Variant Attributes

Field attributes can also be applied to an enum variant. If there are multiple items defined in a single variant then the attribute will be applied to each.

nest! {
    enum MyEnum {
        #>[derive(Debug)]
        Variant {
            // #[derive(Debug)
            one: struct One,
            // #[derive(Debug)
            two: struct Two
        }
    }
}

enum MyEnum {
    Variant {
        one: One,
        two: Two,
    }
}

#[derive(Debug)]
struct One;

#[derive(Debug)]
struct Two;

Semicolons

Rust mandates semicolons to mark the end of tuple struct and unit struct declarations. Nestify, however, introduces flexibility by making this semicolon optional.

Rust Standard

• Tuple struct: struct MyTuple(i32, String);
• Unit struct: struct MyUnit;

Nestify Flexibility

With Nestify, you can omit the semicolon without any impact:

// Unit struct without a semicolon
nest! {
    struct MyUnit
}

// Tuple struct without a semicolon
nest! {
    struct MyTuple(i32, String)
}

struct MyUnit;
//           ^ automaticly added

struct MyTuple(i32, String);
//                         ^ automaticly added

This adjustment simplifies syntax, particularly in the context of defining nested structures, aligning with Nestify's goal of enhancing code readability and maintenance. Whether you include the semicolon or not, Nestify processes the definitions correctly, thanks to its domain-specific optimizations.

Visibility

Visibility can be altered in both parent and nested structures. It exhibits the following behavior

Named Field Visibility

When using named fields, you must specify the desired visibility before both the field and the definition.

nest! {
    pub struct One {
        pub two: pub struct Two
        //|      ^^^ visibility applied to definition (b)
        //|> visibility applied to field (a)
    }
}

pub struct One { 
    pub two: Two,
    //^ (a)
}

pub struct Two;
//^ (b)

Unnamed Field Visibility

Unnamed fields apply visibility to both the field and the item.

nest! {
    pub struct One(pub struct Two)
    //             ^^^ visibility applied to both field and struct
}

pub struct One(pub Two);
//             ^^^ applied here

pub struct Two;
//^ and here

Enum Variants

Enum variants apply visibility just to the structure. This is because variants inherit the base visibility of the enum. See E0449 for more details.

nest! {
    pub enum One {
        Two(pub struct Two)
        //  ^^^ will apply to the structure
    }
}

pub enum One { 
    Two(Two) 
}

pub struct Two;
//^ applied to structure

Generic containers

Nestify also supports defining nested structures inside generic containers like Vec<T>, Option<T>, or Result<T, E>.

struct One(Vec<struct Two { field: i32 }>);

struct One(Vec<Two>);

struct Two {
    field: i32,
}

Here, struct Two is being defined directly within the generic parameter of Vec<T>.

Another Example

To further illustrate, consider a scenario where you want to include an optional configuration struct within another struct:

struct AppConfig(Option<struct DatabaseConfig { url: String }>);

struct AppConfig(Option<DatabaseConfig>);

struct DatabaseConfig {
    url: String,
}

In this example, struct DatabaseConfig is defined directly within the Option<T> generic type in the declaration of AppConfig.

Limitations

Other kinds of indirections are not supported, such as after a & or &mut, inside a fixed size array [_, N] or dynamic size array [_], tuples and probably many others. If you need such indirections feel free to contribute to add support for them.

Contributing

I love contributors! Plus, I'm a bad writer, so I would love community support to improve this guide as well.

[!IMPORTANT] While not required, It is strongly recommended that you either submit an issue or contact me before implementing a feature for the best chance of being accepted

To make code changes:

1. Fork the repository.
2. Create a new branch for your features or bug fixes.
3. Write tests for your changes.
4. Make sure all tests pass.
5. Submit a pull request.

Standard stuff!

License

This project is licensed under the MIT License. If you need it under a different license Contact Me. MIT license support will always be maintained. Don't fear!

Contact me

Check GitHub for information @snowfoxsh

Credits

These wonderful people made major contributions. Check them out

• @nanocryk: Implemented nested definitions in generics