[−][src]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, andGetVariantField
/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 toStructuralExt
. -
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 asmake_struct
to construct anonymous structs
Clarifications
The way that this library emulates structural types is by using traits as bounds or trait objects.
All the structural
traits are dyn-compatible(also known as object-safe),
and no change will be made to make them not dyn-compatible.
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).
Required macros
The only macros that are required to use this crate are the ones for TStr
,
every other macro expands to code that can be written manually.
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 |
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 |
make_struct | Constructs an anonymous struct, which implements all the accessor traits for its field. |
structural_alias | The |
switch | Provides basic pattern matching for structural enums. |
ts | Constructs a
|
tstr_aliases | Declares type aliases for |
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 |
z_impl_box_into_variant_field_method | For use in manual implementations of the |
z_raw_borrow_enum_field | For creating a raw pointer of an enum field,as either |
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 |
Structs
FieldPathSet | A list of field paths to access multiple fields,
whose uniqueness is determined by the |
NestedFieldPath | A type-level representation of a chain of field accesses,like |
NestedFieldPathSet | Allows accessing multiple fields inside of some nested field. |
StrucWrapper | A wrapper-type alternative to |
TStr | Type-level string,used for identifiers in field paths. |
VariantField | This allows accessing the |
VariantName | This allows accessing the |
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 |