Object to Object mapper for Rust

o2o procedural macro is able to generate implementation of 6 kinds of traits:

// #[from_owned()]
impl std::convert::From<A> for B { ... }

// #[from_ref()]
impl std::convert::From<&A> for B { ... }

// #[owned_into()]
impl std::convert::Into<A> for B { ... }

// #[ref_into()]
impl std::convert::Into<A> for &B { ... }

// #[owned_into_existing()]
impl o2o::traits::IntoExisting<A> for B { ... }

// #[ref_into_existing()]
impl o2o::traits::IntoExisting<A> for &B { ... }

It also has shortcuts to configure multiple trait implementations with fewer lines of code:

	#[map()]	#[from()]	#[into()]	#[map_owned()]	#[map_ref()]	#[into_existing()]
#[from_owned()]	✔️	✔️	❌	✔️	❌	❌
#[from_ref()]	✔️	✔️	❌	❌	✔️	❌
#[owned_into()]	✔️	❌	✔️	✔️	❌	❌
#[ref_into()]	✔️	❌	✔️	❌	✔️	❌
#[owned_into_existing()]	❌	❌	❌	❌	❌	✔️
#[ref_into_existing()]	❌	❌	❌	❌	❌	✔️

With that, let's look at some examples.

Examples

Simplest Case

use o2o::o2o;

struct Entity {
    some_int: i32,
    another_int: i16,
}

#[derive(o2o)]
#[map_owned(Entity)]
struct EntityDto {
    some_int: i32,
    another_int: i16,
}

impl std::convert::From<Entity> for EntityDto {
    fn from(value : Entity) -> EntityDto {
        EntityDto { 
            some_int : value.some_int, 
            another_int : value.another_int, 
        }
     }
}

impl std::convert::Into<Entity> for EntityDto {
    fn into(self) -> Entity {
        Entity {
            some_int : self.some_int,
            another_int : self.another_int,
        }
    }
}

With the above code you should be able to do this:

let entity = Entity { some_int: 123, another_int: 321 }
let dto: EntityDto = entity.into();
// and this:
let dto = EntityDto { some_int: 123, another_int: 321 }
let entity: Entity = dto.into();

Different field name

struct Entity {
    some_int: i32,
    another_int: i16,
}

#[derive(o2o)]
#[from_ref(Entity)]
#[ref_into_existing(Entity)]
struct EntityDto {
    some_int: i32,
    #[map(another_int)]
    different_int: i16,
}

impl std::convert::From<&Entity> for EntityDto {
    fn from(value : & Entity) -> EntityDto {
        EntityDto { 
            some_int : value.some_int,
            different_int : value.another_int,
        }
    }
}

impl o2o::traits::IntoExisting<Entity> for &EntityDto {
    fn into_existing(self, other : &mut Entity) {
        other.some_int = self.some_int; 
        other.another_int = self.different_int;
    }
}

Different field type

struct Entity {
    some_int: i32,
    val: i16,
    str: String
}

#[derive(o2o)]
#[map(Entity)]
struct EntityDto {
    some_int: i32,
    #[from(~.to_string())] // Tilde allows to append code at the end of the right side of field initialization for From<T> impls
    #[into(~.parse::<i16>().unwrap())] // here it's the same but for Into<T> impls
    val: String,
    // Here Into and From are symmetric, so it has to be only specified once.
    // Note that .clone() is only needed for borrowing impls, so we use #[map_ref()]
    #[map_ref(~.clone())] 
    str: String
}

impl std :: convert :: From < Entity > for EntityDto {
    fn from(value : Entity) -> EntityDto {
        EntityDto {
            some_int: value.some_int,
            val: value.val.to_string(),
            str: value.str, // no .clone() needed
        }
    }
}
impl std :: convert :: From < & Entity > for EntityDto {
    fn from(value : & Entity) -> EntityDto {
        EntityDto {
            some_int: value.some_int,
            val: value.val.to_string(),
            str: value.str.clone(),
        }
    }
}
impl std::convert::Into<Entity> for EntityDto {
    fn into(self) -> Entity {
        Entity {
            some_int: self.some_int,
            val: self.val.parse::<i16>().unwrap(),
            str: self.str, // no .clone() needed
        }
    }
}
impl std::convert::Into<Entity> for &EntityDto {
    fn into(self) -> Entity {
        Entity {
            some_int: self.some_int,
            val: self.val.parse::<i16>().unwrap(),
            str: self.str.clone(),
        }
    }
}

Nested structs

struct Entity {
    some_int: i32,
    child: Child,
}
struct Child {
    child_int: i32,
}

#[derive(o2o)]
#[from_owned(Entity)]
struct EntityDto {
    some_int: i32,
    #[map(~.into())]
    child: ChildDto
}

#[derive(o2o)]
#[from_owned(Child)]
struct ChildDto {
    child_int: i32,
}

impl std::convert::From<Entity> for EntityDto {
    fn from(value : Entity) -> EntityDto { 
        EntityDto { 
            some_int: value.some_int, 
            child: value.child.into(), 
        }
    }
}

impl std::convert::From<Child> for ChildDto {
    fn from(value : Child) -> ChildDto { 
        ChildDto { 
            child_int: value.child_int, 
        }
    }
}

Nested collection

struct Entity {
    some_int: i32,
    children: Vec<Child>,
}
struct Child {
    child_int: i32,
}

#[derive(o2o)]
#[map_owned(Entity)]
struct EntityDto {
    some_int: i32,
    // Here field name as well as type are different, so we pass in field name and tilde inline expression.
    // Also, it doesn't hurt to use member level instruction #[map()], 
    // which is broader than struct level instruction #[map_owned]
    #[map(children, ~.iter().map(|p|p.into()).collect())]
    children_vec: Vec<ChildDto>
}

#[derive(o2o)]
#[map_ref(Child)]
struct ChildDto {
    child_int: i32,
}

impl std::convert::From<Entity> for EntityDto {
    fn from(value : Entity) -> EntityDto {
        EntityDto {
            some_int: value.some_int, 
            children_vec: value.children.iter().map(|p|p.into()).collect(),
        }
    }
} 
impl std::convert::Into<Entity> for EntityDto {
    fn into(self) -> Entity {
        Entity {
            some_int: self.some_int, 
            children: self.children_vec.iter().map(| p | p.into()).collect(),
        }
    }
}
impl std::convert::From<&Child> for ChildDto {
    fn from(value : & Child) -> ChildDto { 
        ChildDto { child_int : value.child_int, } 
    }
} 
impl std::convert::Into<Child> for &ChildDto {
    fn into(self) -> Child { 
        Child { child_int : self.child_int, }
    }
}

Assymetric fields (skipping and providing default values)

o2o is able to handle scenarios when either of the structs has a field that the other struct doesn't have.

For the scenario where you put o2o instructions on a struct that contains extra field:

struct Person {
    id: i32,
    full_name: String,
    age: i8,
}

#[derive(o2o)]
#[map_owned(Person)]
struct PersonDto {
    id: i32,
    full_name: String,
    age: i8,
    // (|| None) below provides default value when creating PersonDto from Person
    // It could have been omited if we only needed to create Person from PersonDto
    #[ghost(|| None)]
    zodiac_sign: Option<ZodiacSign>
}
enum ZodiacSign {}

impl std::convert::From<Person> for PersonDto {
    fn from(value : Person) -> PersonDto {
        PersonDto {
            id: value.id, 
            full_name: value.full_name, 
            age: value.age,
            zodiac_sign: (|| None) (),
        }
    }
}
impl std::convert::Into<Person> for PersonDto {
    fn into(self) -> Person { 
        Person {
            id: self.id,
            full_name: self.full_name,
            age: self.age, 
        }
    }
}

In a reverse case, you need to use a struct level #[ghost()] instruction:

#[derive(o2o)]
#[map_owned(PersonDto)]
#[ghost(zodiac_sign: || { None })] // #[ghost()] struct level instruction accepts only braced closures.
struct Person {
    id: i32,
    full_name: String,
    age: i8,
}

struct PersonDto {
    id: i32,
    full_name: String,
    age: i8,
    zodiac_sign: Option<ZodiacSign>
}
enum ZodiacSign {}

impl std::convert::From<PersonDto> for Person {
    fn from(value : PersonDto) -> Person {
        Person {
            id: value.id,
            full_name: value.full_name,
            age: value.age,
        }
    }
} 
impl std::convert::Into<PersonDto> for Person {
    fn into(self) -> PersonDto {
        PersonDto {
            id: self.id,
            full_name: self.full_name,
            age: self.age,
            zodiac_sign: (| | { None }) (),
        }
    }
}

Slightly complex example

struct Employee {
    id: i32,
    first_name: String,
    last_name: String,
    subordinate_of: Box<Employee>,
    subordinates: Vec<Box<Employee>>
}
impl Employee {
    fn get_full_name(&self) -> String {
        format!("{} {}", self.first_name, self.last_name)
    }
}

#[derive(o2o)]
#[map(Employee)]
#[ghost(
    // o2o supports closures with one input parameter.
    // This parameter represents instance on the other side of the conversion.
    first_name: |x| {x.get_first_name()},
    last_name: |x| {x.get_last_name()}
)]
struct EmployeeDto {
    #[map(id)]
    employee_id: i32,
    // '@.' is another flavor of 'inline expression'. 
    // @ also represents instance on the other side of the conversion.
    #[ghost(@.get_full_name())]
    full_name: String,

    #[from(|x| Box::new(x.subordinate_of.as_ref().into()))]
    #[into(subordinate_of, |x| Box::new(x.reports_to.as_ref().into()))]
    reports_to: Box<EmployeeDto>,

    #[map(~.iter().map(|p|Box::new(p.as_ref().into())).collect())]
    subordinates: Vec<Box<EmployeeDto>>
}
impl EmployeeDto {
    fn get_first_name(&self) -> String {
        self.full_name.split_whitespace().collect::<Vec<&str>>()[0].into()
    }
    fn get_last_name(&self) -> String {
        self.full_name.split_whitespace().collect::<Vec<&str>>()[1].into()
    }
}

impl std::convert::From<Employee> for EmployeeDto {
    fn from(value : Employee) -> EmployeeDto {
        EmployeeDto {
            employee_id: value.id,
            full_name: value.get_full_name(),
            reports_to: (|x: &Employee| Box::new(x.subordinate_of.as_ref().into()))(&value),
            subordinates: value.subordinates.iter().map(|p| Box::new(p.as_ref().into())).collect(),
        }
    }
} 
impl std::convert::From<&Employee> for EmployeeDto {
    fn from(value : & Employee) -> EmployeeDto {
        EmployeeDto {
            employee_id: value.id,
            full_name: value.get_full_name(),
            reports_to: (|x: &Employee | Box::new(x.subordinate_of.as_ref().into()))(value),
            subordinates: value.subordinates.iter().map(|p| Box::new(p.as_ref().into())).collect(),
        }
    }
}
impl std::convert::Into<Employee> for EmployeeDto {
    fn into(self) -> Employee {
        Employee {
            id : self.employee_id,
            subordinate_of: (|x: &EmployeeDto | Box::new(x.reports_to.as_ref().into()))(& self),
            subordinates: self.subordinates.iter().map(|p| Box::new(p.as_ref().into())).collect(), 
            first_name: (|x: &EmployeeDto | { x.get_first_name() })(&self),
            last_name: (|x: &EmployeeDto | { x.get_last_name() })(&self),
        }
    }
}
impl std::convert::Into<Employee> for &EmployeeDto {
    fn into(self) -> Employee {
        Employee {
            id : self.employee_id,
            subordinate_of: (|x : &EmployeeDto | Box::new(x.reports_to.as_ref().into()))(self),
            subordinates: self.subordinates.iter().map(|p| Box::new(p.as_ref().into())).collect(),
            first_name: (|x: &EmployeeDto | { x.get_first_name() })(self),
            last_name : (|x: &EmployeeDto | { x.get_last_name() })(self),
        }
    }
}

Flatened children

When the instructions are put on the side that contains flatened properties, conversion From<T> and IntoExisting<T> only requires usage of a member level #[child(...)] instruction, which accepts a path to the unflatened field (without the field name itself).

struct Car {
    number_of_doors: i8,
    vehicle: Vehicle
}
struct Vehicle {
    number_of_seats: i16,
    machine: Machine,
}
struct Machine {
    brand: String,
    year: i16
}

#[derive(o2o)]
#[from_owned(Car)]
#[into_existing(Car)]
struct CarDto {
    number_of_doors: i8,

    #[child(vehicle)]
    number_of_seats: i16,

    #[child(vehicle.machine)]
    #[map_ref(~.clone())]
    brand: String,

    #[child(vehicle.machine)]
    year: i16
}

impl std::convert::From<Car> for CarDto {
    fn from(value: Car) -> CarDto {
        CarDto {
            number_of_doors: value.number_of_doors,
            number_of_seats: value.vehicle.number_of_seats,
            brand: value.vehicle.machine.brand, 
            year: value.vehicle.machine.year,
        }
    }
}
impl o2o::traits::IntoExisting<Car> for &CarDto {
    fn into_existing(self, other: &mut Car) {
        other.number_of_doors = self.number_of_doors;
        other.vehicle.number_of_seats = self.number_of_seats;
        other.vehicle.machine.brand = self.brand.clone();
        other.vehicle.machine.year = self.year;
    }
}

When you need an Into<T> conversion, o2o also expects you to provide types for flatened properties via struct level #[children(...)] instruction:

#[derive(o2o)]
#[owned_into(Car)]
#[children(vehicle: Vehicle, vehicle.machine: Machine)]
struct CarDto {
    number_of_doors: i8,

    #[child(vehicle)]
    number_of_seats: i16,

    #[child(vehicle.machine)]
    brand: String,

    #[child(vehicle.machine)]
    year: i16
}

impl std::convert::Into<Car> for CarDto {
    fn into(self) -> Car {
        Car {
            number_of_doors: self.number_of_doors,
            vehicle: Vehicle {
                number_of_seats: self.number_of_seats, 
                machine: Machine {
                    brand: self.brand,
                    year: self.year,
                },
            },
        }
    }
}

The reverse case, where you have to put o2o insturctions on the side that has field that are being flatened, is slightly tricky:

#[derive(o2o)]
#[owned_into(CarDto)]
struct Car {
    number_of_doors: i8,
    #[parent]
    vehicle: Vehicle
}

#[derive(o2o)]
#[owned_into_existing(CarDto)]
struct Vehicle {
    number_of_seats: i16,
    #[parent]
    machine: Machine,
}

#[derive(o2o)]
#[owned_into_existing(CarDto)]
struct Machine {
    brand: String,
    year: i16
}

// CarDto has to implement `Default` trait in this case.
#[derive(Default)]
struct CarDto {
    number_of_doors: i8,
    number_of_seats: i16,
    brand: String,
    year: i16
}

impl std::convert::Into<CarDto> for Car {
    fn into(self) -> CarDto {
        let mut obj = CarDto {
            number_of_doors: self.number_of_doors, 
            .. Default::default() 
        };
        self.vehicle.into_existing(& mut obj) ; obj
    }
}
impl o2o :: traits :: IntoExisting < CarDto > for Vehicle {
    fn into_existing(self, other : & mut CarDto) {
        other.number_of_seats = self.number_of_seats;
        self.machine.into_existing(other);
    }
}
impl o2o :: traits :: IntoExisting < CarDto > for Machine {
    fn into_existing(self, other : & mut CarDto) {
        other.brand = self.brand;
        other.year = self.year;
    }
}

Tuple structs

struct TupleEntity(i32, String);

#[derive(o2o)]
#[map_ref(TupleEntity)]
struct TupleEntityDto(i32, #[map_ref(~.clone())] String);

impl std :: convert :: From < & TupleEntity > for TupleEntityDto {
    fn from(value : & TupleEntity) -> TupleEntityDto {
        TupleEntityDto(value.0, value.1.clone(),)
    }
}
impl std :: convert :: Into < TupleEntity > for & TupleEntityDto {
    fn into(self) -> TupleEntity {
        TupleEntity(self.0, self.1.clone(),)
    }
}

As long as Rust allows following syntax, easy conversion between tuple and named structs can be done if placing o2o instructions on named side:

struct TupleEntity(i32, String);

#[derive(o2o)]
#[map_ref(TupleEntity)]
struct EntityDto {
    #[map_ref(0)]
    some_int: i32, 
    #[map_ref(1, ~.clone())]
    some_str: String
}

impl std::convert::From<&TupleEntity> for EntityDto {
    fn from(value: & TupleEntity) -> EntityDto {
        EntityDto { 
            some_int: value.0,
            some_str: value.1.clone(),
        }
    }
}
impl std::convert::Into<TupleEntity> for &EntityDto {
    fn into(self) -> TupleEntity {
        TupleEntity {
            0 : self.some_int,
            1: self.some_str.clone(),
        }
    }
}

Struct kind hints

By default, o2o will suppose that the struct on the other side is the same kind of struct that the original one is. In order to convert between named and tuple structs when you need to place instructions on a tuple side, you`ll need to use Struct Kind Hint:

#[derive(o2o)]
#[map_owned(EntityDto as {})]
struct TupleEntity(#[map(some_int)] i32, #[map(some_str)] String);

struct EntityDto{
    some_int: i32, 
    some_str: String
}

impl std :: convert :: From < EntityDto > for TupleEntity {
    fn from(value : EntityDto) -> TupleEntity {
        TupleEntity(value.some_int, value.some_str,)
    }
}
impl std :: convert :: Into < EntityDto > for TupleEntity {
    fn into(self) -> EntityDto { 
        EntityDto {
            some_int : self.0,
            some_str : self.1,
        }
    }
}

Generics

struct Entity<T> {
    some_int: i32,
    something: T,
}

#[derive(o2o)]
#[map_owned(Entity::<f32>)]
struct EntityDto {
    some_int: i32,
    something: f32
}

impl std::convert::From<Entity::<f32>> for EntityDto {
    fn from(value: Entity::<f32>) -> EntityDto {
        EntityDto {
            some_int: value.some_int, 
            something: value.something,
        }
    }
}
impl std::convert::Into<Entity::<f32>> for EntityDto {
    fn into(self) -> Entity::<f32> {
        Entity::<f32> {
            some_int: self.some_int,
            something: self.something,
        }
    }
}

Where clauses

struct Child<T> {
    child_int: i32,
    something: T,
}

#[derive(o2o)]
#[map_owned(Child::<T>)]
#[where_clause(T: Clone)]
struct ChildDto<T> {
    child_int: i32,
    #[map(something, ~.clone())]
    stuff: T,
}

impl <T> std::convert::From<Child::<T>> for ChildDto<T> where T: Clone {
    fn from(value: Child::<T>) -> ChildDto<T> {
        ChildDto {
            child_int: value.child_int,
            stuff: value.something.clone(),
        }
    }
}
impl <T> std::convert::Into<Child::<T>> for ChildDto <T> where T: Clone {
    fn into(self) -> Child::<T> {
        Child::<T> {
            child_int: self.child_int,
            something: self.stuff.clone(),
        }
    }
}

Mapping to multiple structs

to be documented...

Avoiding proc macro attribute name collisions (alternative instruction syntax)

to be documented...

Additional o2o shortcuts available via #[o2o(...)] syntax

to be documented...

#[panic_debug_info] instruction

to be documented...

Contributions

All issues, questions, pull requests are extremely welcome.

License