Crate structural

This library provides field accessor traits,and emulation of structural types.

Features

These are some of the features this library provides:

• Structural derive macro to implement accessor traits for every public field: GetField/GetFieldMut/IntoField for structs, and GetVariantField/GetVariantFieldMut/IntoVariantField for enums.

• The StructuralExt extension trait,which defines the main methods to access fields, so long as the type implements the accessor traits for those fields.

• The StrucWrapper wrapper type,defined as an alternative to StructuralExt.

• The structural_alias macro, to declare trait aliases for accessor traits, using field-in-trait syntax.

• The impl_struct macro to declare structural parameter/return types, as well as make_struct to construct anonymous structs

Clarifications

The way that this library emulates structural types is by using traits as bounds or trait objects.

By default all structural types are open, structs and enums can have more variants and or fields than are required.

The only exception to this is exhaustive enums, in which the variant count and names must match exactly, this is useful for exhaustive matching of variants (in the switch macro).

Conditional methods

*box_* methods

Every *Into*Field* trait has a *box_* method that takes a Box<_> parameter which only exists when the "alloc" feature is enabled (it is enabled by default).

If you don't enable the "alloc" feature yourself (it is enabled by default), you must implement those methods using the macros indicated in the Features section of the documentation for each trait

For an example of how to use those macros, you can look at the examples in the docs for each of the *Into*Field* traits.

Examples

Structural Derive for structs

This demonstrates how you can use any type with a superset of the fields of another one in a function.

Structural derive macro docs for more details on derivation.

use structural::{StructuralExt,Structural,fp};


fn reads_point4<S>(point:&S)
where
    // The `Structural` derive generated the `Point3D_SI` trait for `Point3D`,
    // aliasing the accessor traits for it.
    S:Point3D_SI<u32>
{
    let (a,b,c)=point.fields(fp!( x, y, z ));

    assert_eq!(a,&0);
    assert_eq!(b,&11);
    assert_eq!(c,&33);
}

fn main(){
    reads_point4(&Point3D { x: 0, y: 11, z: 33 });

    reads_point4(&Point4D {
        x: 0,
        y: 11,
        z: 33,
        a: 0xDEAD,
    });

    reads_point4(&Point5D {
        x: 0,
        y: 11,
        z: 33,
        a: 0xDEAD,
        b: 0xBEEF,
    });
}


#[derive(Structural)]
// Using the `#[struc(public)]` attribute tells the derive macro to
// generate the accessor trait impls for non-`pub` fields.
#[struc(public)]
struct Point3D<T>{
    x:T,
    y:T,
    z:T,
}

#[derive(Structural)]
// By default only public fields get accessor trait impls,
// using `#[struc(public)]` you can have impls to access private fields.
#[struc(public)]
struct Point4D<T>{
    x:T,
    y:T,
    z:T,
    a:T,
}

#[derive(Structural)]
struct Point5D<T>{
    pub x:T,
    pub y:T,
    pub z:T,
    pub a:T,
    pub b:T,
}

Structural Derive for enums

This demonstrates how you can use structural enums.

For details on enums look here.

use structural::{StructuralExt,Structural,fp,switch};

fn main(){
    {
        // Command

        run_command(Command::SendEmail(SendEmail{
            to:"ferris@lib.rs".to_string(),
            content:"Hello".to_string(),
        }));
        run_command(Command::RemoveAddress("gopher".to_string()));
    }
    {
        // ExtraCommand
        //
        // ExtraCommand can't be passed to `run_command` because that function requires
        // an enum with exactly the `SendEmail` and `RemoveAddress` variants.

        // The `SendEmail` variant can have more fields than the one in the `Command` enum,
        // they're just ignored.
        run_command_nonexhaustive(ExtraCommand::SendEmail{
            to:"squatter@crates.io".to_string(),
            content:"Can you stop squatting crate names?".to_string(),
            topic:"squatting".to_string(),
        }).unwrap();

        let ra_cmd=ExtraCommand::RemoveAddress("smart_person".to_string());
        run_command_nonexhaustive(ra_cmd).unwrap();

        let ca_cmd=ExtraCommand::CreateAddress("honest_person".to_string());
        let res=run_command_nonexhaustive(ca_cmd.clone());
        assert_eq!( res, Err(UnsupportedCommand(ca_cmd)) );
    }
}

// Runs the passed in command.
//
// The `Command_ESI` trait allows only enums with the same variants as
// `Command` to be passed in(they can have a superset of the fields in `Command`).
fn run_command<S>(cmd:S)
where
    S:Command_ESI
{
    run_command_nonexhaustive(cmd)
        .ok()
        .expect("`run_command_nonexhaustive` must match all `Command` variants")
}

// Runs the passed in command.
//
// The `Command_SI` trait allows enums with a superset of the variants in `Command`
// to be passed in,
// requiring the a `_=>` branch when it's matched on with the `switch` macro.
fn run_command_nonexhaustive<S>(cmd:S)->Result<(),UnsupportedCommand<S>>
where
    S:Command_SI
{
    switch!{cmd;
        // This matches the SendEmail variant and destructures it into the
        // `to` and `content` fields (by reference,because of the `ref`).
        ref SendEmail{to,content}=>{
            println!("Sending message to the '{}' email address.",to);
            println!("Content:{:?}",content);
            Ok(())
        }
        // `cmd` is moved into the branch here,
        // wrapped into a `VariantProxy<S,TS!(RemoveAddress)>`,
        // which allows direct access to the fields in the variant.
        //
        // This does not destructure the variant because
        // it's not possible to unwrap a structural type into multiple fields yet
        // (special casing the single field case doesn't seem like a good idea).
        RemoveAddress=>{
            let address=cmd.into_field(fp!(0));
            println!("removing the '{}' email address",address);
            Ok(())
        }
        _=>Err(UnsupportedCommand(cmd))
    }
}

#[derive(Structural)]
enum Command{
    // The `newtype(bounds="...")` attribute marks the variant as being a newtype variant,
    // delegating field accessors for the variant to `SendEmail`(its one field),
    // as well as replacing the bounds for the variant in the generated
    // `Command_SI` and `Command_ESI` traits with `SendEmail_VSI<TS!(SendEmail)>`.
    //
    // `SendEmail_VSI` was generated by the `Structural` derive on `SendEmail`,
    // with accessor trait bounds for accessing the struct's fields
    // in a variant (it takes the name of the variant as a generic parameter).
    #[struc(newtype(bounds="SendEmail_VSI<@variant>"))]
    SendEmail(SendEmail),
    RemoveAddress(String),
}

#[derive(Structural)]
pub struct SendEmail{
    pub to: String,
    pub content: String,
}

#[derive(Debug,Structural,Clone,PartialEq)]
// This attribute stops the generation of the
// `ExtraCommands_SI` and `ExtraCommands_ESI` traits
#[struc(no_trait)]
pub enum ExtraCommand{
    SendEmail{
        to: String,
        content: String,
        topic: String,
    },
    RemoveAddress(String),
    CreateAddress(String),
}

#[derive(Debug,PartialEq)]
pub struct UnsupportedCommand<T>(pub T);

Structural alias for struct

This demonstrates how you can define a trait aliasing field accessors, using a fields-in-traits syntax.

For more details you can look at the docs for the structural_alias macro.

use structural::{StructuralExt,Structural,structural_alias,fp};

use std::borrow::Borrow;

structural_alias!{
    trait Person<H:House>{
        name:String,
        house:H,
    }

    trait House{
        dim:Dimension3D,
    }
}


fn print_name<T,H>(this:&T)
where
    T:?Sized+Person<H>,
    H:House,
{
    let (name,house_dim)=this.fields(fp!( name, house.dim ));
    println!("Hello, {}!", name);

    let (w,h,d)=house_dim.fields(fp!( width, height, depth ));

    if w*h*d >= 1_000_000 {
        println!("Your house is enormous.");
    }else{
        println!("Your house is normal sized.");
    }
}

// most structural aliases are object safe
fn print_name_dyn<H>(this:&dyn Person<H>)
where
    H:House,
{
    print_name(this)
}



#[derive(Structural)]
#[struc(public)]
struct Dimension3D{
    width:u32,
    height:u32,
    depth:u32,
}

//////////////////////////////////////////////////////////////////////////
////          The stuff here could be defined in a separate crate


fn main(){
    let worker=Worker{
        name:"John Doe".into(),
        salary:Cents(1_000_000_000_000_000),
        house:Mansion{
            dim:Dimension3D{
                width:300,
                height:300,
                depth:300,
            },
            money_vault_location:"In the basement".into(),
        }
    };

    let student=Student{
        name:"Jake English".into(),
        birth_year:1995,
        house:SmallHouse{
            dim:Dimension3D{
                width:30,
                height:30,
                depth:30,
            },
            residents:10,
        }
    };

    print_name(&worker);
    print_name(&student);

    print_name_dyn(&worker);
    print_name_dyn(&student);
}


#[derive(Structural)]
// Using the `#[struc(public)]` attribute tells the derive macro to
// generate the accessor trait impls for non-`pub` fields.
#[struc(public)]
struct Worker{
    name:String,
    salary:Cents,
    house:Mansion,
}

#[derive(Structural)]
#[struc(public)]
struct Student{
    name:String,
    birth_year:u32,
    house:SmallHouse,
}


#[derive(Structural)]
#[struc(public)]
struct Mansion{
    dim:Dimension3D,
    money_vault_location:String,
}

#[derive(Structural)]
#[struc(public)]
struct SmallHouse{
    dim:Dimension3D,
    residents:u32,
}

Structural alias for enums

This demonstrates how you can use structural aliases for enums.

This shows both exhaustive and nonexhaustive enum structural aliases.

For more details you can look at the docs for the structural_alias macro.

use structural::{StructuralExt,Structural,structural_alias,switch,fp};
use std::fmt::Debug;

pet_animal_ex(&SomeMammals::Dog{years:1,volume_cm3:1});
pet_animal_ex(&SomeMammals::Horse);

// `MoreAnimals` cannot be passed to `pet_animal_ex`
// since that function requires an enum with only `Dog` and `Horse` variants.
assert_eq!( pet_animal(&MoreAnimals::Dog{years:10,volume_cm3:100}), Ok(()) );
assert_eq!( pet_animal(&MoreAnimals::Horse), Ok(()) );
assert_eq!( pet_animal(&MoreAnimals::Cat{lives:9}), Err(CouldNotPet) );
assert_eq!( pet_animal(&MoreAnimals::Seal), Err(CouldNotPet) );

fn pet_animal(animal: &dyn Animal)-> Result<(),CouldNotPet> {
    // `::Dog` accesses the `Dog` variant
    // (without the `::` it'd be interpreted as a field access),
    // The `=>` allows getting multiple fields from inside a nested field
    // (this includes enum variants).
    // `years,volume_cm3` are the field accessed from inside `::Dog`
    let dog_fields = fp!(::Dog=>years,volume_cm3);

    if animal.is_variant(fp!(Horse)) {
        println!("You are petting the horse");
    }else if let Some((years,volume_cm3))= animal.fields(dog_fields) {
        println!("You are petting the {} year old,{} cm³ dog",years,volume_cm3);
    }else{
        return Err(CouldNotPet);
    }
    Ok(())
}

// This can't take a `&dyn Animal_Ex` because traits objects don't
// automatically support upcasting into other trait objects
// (except for auto traits like Send and Sync ).
fn pet_animal_ex(animal: &impl Animal_Ex) {
    pet_animal(animal)
        .expect("`pet_animal` must match on all variants from the `Animal` trait");
}

// The same as `pet_animal` ,except that this uses a `switch`
fn pet_animal_switch(animal: &dyn Animal)-> Result<(),CouldNotPet> {
    switch!{animal;
        ref Horse=>{
            println!("You are petting the horse");
        }
        ref Dog{years,volume_cm3}=>{
            println!("You are petting the {} year old,{} cm³ dog",years,volume_cm3);
        }
        _=>return Err(CouldNotPet)
    }
    Ok(())
}


#[derive(Debug,PartialEq)]
struct CouldNotPet;

structural_alias!{
    // The `#[struc(and_exhaustive_enum(suffix="_Ex"))]` attribute
    // generates the `Animal_Ex` trait with this trait as a supertrait,
    // and with the additional requirement that the enum
    // only has the `horse` and `Dog` variants
    // (They variants can still have more fields than required).
    //
    // structural aliases can have supertraits,here it's `Debug`
    #[struc(and_exhaustive_enum(suffix="_Ex"))]
    trait Animal: Debug{
        Horse,
        Dog{years:u16,volume_cm3:u64},
    }
}


#[derive(Debug,Structural)]
enum SomeMammals{
    Horse,
    Dog{years:u16,volume_cm3:u64},
}

#[derive(Debug,Structural)]
enum MoreAnimals{
    Cat{lives:u8},
    Dog{years:u16,volume_cm3:u64},
    Horse,
    Seal,
}

Anonymous structs (make_struct macro)

This demonstrates how you can construct an anonymous struct.

For more details you can look at the docs for the make_struct macro.

Docs for the impl_struct macro macro.

use structural::{StructuralExt,fp,impl_struct,make_struct,structural_alias};

structural_alias!{
    trait Person<T>{
        // We only have shared access (`&String`) to the field.
        ref name:String,

        // We have shared,mutable,and by value access to the field.
        // Not specifying any of `mut`/`ref`/`move` is equivalent to `mut move value:T,`
        value:T,
    }
}

fn make_person(name:String)-> impl_struct!{ ref name:String, value:() } {
    make_struct!{
        name,
        value: (),
    }
}


fn print_name(mut this: impl_struct!{ ref name:String, value:Vec<String> } ) {
    println!("Hello, {}!",this.field_(fp!(name)) );

    let list=vec!["what".into()];
    *this.field_mut(fp!(value))=list.clone();
    assert_eq!( this.field_(fp!(value)), &list );
    assert_eq!( this.into_field(fp!(value)), list );
}


// most structural aliases are object safe
//
// This has to use the Person trait,
// since `impl_struct!{....}` expands to `impl Trait0+Trait0+etc`
fn print_name_dyn(this:&mut dyn Person<Vec<String>>){
    println!("Hello, {}!",this.field_(fp!(name)) );

    let list=vec!["what".into()];
    *this.field_mut(fp!(value))=list.clone();
    assert_eq!( this.field_(fp!(value)), &list );
}

//////////////////////////////////////////////////////////////////////////
////          The stuff here could be defined in a separate crate

fn main(){
    let worker=make_struct!{
        // This derives clone for the anonymous struct
        #![derive(Clone)]
        name:"John Doe".into(),
        salary:Cents(1_000_000_000_000_000),
        value:vec![],
    };

    let student=make_struct!{
        // This derives clone for the anonymous struct
        #![derive(Clone)]
        name:"Jake English".into(),
        birth_year:1995,
        value:vec![],
    };

    print_name(worker.clone());
    print_name(student.clone());

    print_name_dyn(&mut worker.clone());
    print_name_dyn(&mut student.clone());

    let person=make_person("Louis".into());

    assert_eq!( person.field_(fp!(name)), "Louis" );
    assert_eq!( person.field_(fp!(value)), &() );
}

#[derive(Debug,Copy,Clone,PartialEq,Eq)]
struct Cents(u64);

Re-exports

pub extern crate std;

pub extern crate alloc;

pub use crate::field::FieldType;

pub use crate::field::GetField;

pub use crate::field::GetFieldMut;

pub use crate::field::GetFieldType;

pub use crate::field::GetFieldType2;

pub use crate::field::GetFieldType3;

pub use crate::field::GetFieldType4;

pub use crate::field::GetVariantField;

pub use crate::field::GetVariantFieldMut;

pub use crate::field::GetVariantFieldType;

pub use crate::field::IntoField;

pub use crate::field::IntoFieldMut;

pub use crate::field::IntoVariantField;

pub use crate::field::IntoVariantFieldMut;

Modules

docs	Documentation for proc-macros and guides.
enums	Enum related traits and types.
field	Accessor and extension traits for fields.
for_examples	Structural-deriving types used in examples,
path	Types used to refer to the field(s) that one is accessing.
reexports	Reexports from other crates.
type_level	types that represent values.
utils	Some helper functions.

Macros

FP	Constructs a field path type for use as a generic parameter.
TS	For getting the type of a TStr<_> (type-level string).
field_path_aliases	Declares aliases for field paths,used to access fields.
fp	Constructs a field path value, which determines the field(s) accessed in StructuralExt methods.
impl_struct	For declaring an anonymous structural type,this expands to an impl Trait.
make_struct	Constructs an anonymous struct, which implements all the accessor traits for its field.
structural_alias	The structural_alias macro defines a trait alias for multiple field accessors.
switch	Provides basic pattern matching for structural enums.
ts	Constructs a TStr value,a type-level string used for identifiers in field paths.
tstr_aliases	Declares type aliases for TStr<_>(type-level string).
unsafe_delegate_structural_with	This macro allows delegating the implementation of the accessor traits.
z_impl_box_into_field_method	For use in manual implementations of the IntoField trait.
z_impl_box_into_variant_field_method	For use in manual implementations of the IntoVariantField trait.
z_raw_borrow_enum_field	For creating a raw pointer of an enum field,as either Some(NonNull<_>) or None.
z_unsafe_impl_get_field_raw_mut	For semi-manual implementors of the GetFieldMut trait for structs.
z_unsafe_impl_get_vfield_raw_mut_fn	Implements the get_vfield_raw_mut_fn and get_vfield_raw_mut_unchecked_fn methods from the GetVariantFieldMut trait.

Structs

FieldPathSet	A list of field paths to access multiple fields, whose uniqueness is determined by the U type parameter.
NestedFieldPath	A type-level representation of a chain of field accesses,like .a.b.c.d.
NestedFieldPathSet	Allows accessing multiple fields inside of some nested field.
StrucWrapper	A wrapper-type alternative to StructuralExt, with methods for accessing fields in structural types.
TStr	Type-level string,used for identifiers in field paths.
VariantField	This allows accessing the F field inside the V enum variant.
VariantName	This allows accessing the V enum variant (by constructing a VariantProxy representing that variant).

Traits

Structural	Marker trait for types that implement some field accessor traits.
StructuralExt	A trait defining the primary way to call methods from structural traits.

Derive Macros

Structural

This macro is documented in structural::docs::structural_macro