[−][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 -
The
FromStructural
andTryFromStructural
conversion traits, similar (but not identical) to the standard libraryFrom
andTryFrom
traits for structural types.
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).
Every trait with the _SI
/_ESI
/_VSI
suffixes in the examples are traits
generated by the Structural
derive macro.
These traits alias the accessor traits implemented by the type they're named after.
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
(except for the __TS
type,
that is an implementation detail that only macros from
this crate should use by name).
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::{fp, Structural, StructuralExt}; fn reads_point3<S>(point: &S) where // The `Point3D_SI` trait was generated by the `Structural` derive for `Point3D`, // aliasing the accessor traits implemented by `Point3D`. 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_point3(&Point3D { x: 0, y: 11, z: 33 }); reads_point3(&Point4D { x: 0, y: 11, z: 33, a: 0xDEAD, }); reads_point3(&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::{fp, switch, Structural, StructuralExt}; 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 the // `to` and `content` fields by value. SendEmail{to,content}=>{ println!("Sending message to the '{}' email address.",to); println!("Content:{:?}",content); Ok(()) } // This matches the RemoveAddress variant and destructures it into // the 0th field (by reference,because of the `ref`). ref RemoveAddress(address)=>{ 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 of the variant to `SendEmail`(its one field), // as well as replacing the bounds for the variant in the // trait aliases generated by the `Structural` derive (`Command_SI` and `Command_ESI`) // 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::{fp, structural_alias, FP, IntoFieldMut, Structural, StructuralExt}; 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>, // This is the one trait that `House` requires in its blanket implementation. // `H: House,` is equivalent to this H: IntoFieldMut<FP!(dim), Ty = Dimension3D>, { 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 // This is the one trait that `House` requires in its blanket implementation. // `H: House,` is equivalent to this H: IntoFieldMut<FP!(dim), Ty = Dimension3D>, { 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(Debug, Copy, Clone, PartialEq, Eq)] struct Cents(u64); #[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 std::fmt::Debug; use structural::{fp, structural_alias, switch, Structural, StructuralExt}; fn main() { 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)); } // For an equivalent function that's ergonomic to write, look below for `pet_animal_switch` 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); // The `is_horse` method comes from the `Animal` trait. if animal.is_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 the `switch` macro fn pet_animal_switch(animal: &dyn Animal) -> Result<(), CouldNotPet> { switch! {animal; Horse=>{ println!("You are petting the horse"); } // This matches the Dog variant, // and destructures it into its `years` and `volume_cm3` fields // as references(because of the `ref`) 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 // (Those 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}, // Structural aliases can define extension methods, fn is_horse(&self) -> bool { self.is_variant(fp!(Horse)) } } } #[derive(Debug, Structural)] #[struc(no_trait)] enum SomeMammals { Horse, Dog { years: u16, volume_cm3: u64 }, } #[derive(Debug, Structural)] #[struc(no_trait)] 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.
use structural::{fp, impl_struct, make_struct, structural_alias, StructuralExt}; 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! { 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 + Trait1 + 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)), &()); // Destructuring the anonymous struct by value. // The type annotation here is just to demonstrate that it returns a `String` by value. let (name, value): (String, ()) = person.into_fields(fp!(name, value)); assert_eq!(name, "Louis"); } #[derive(Debug, Copy, Clone, PartialEq, Eq)] struct Cents(u64);
Re-exports
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
convert | Traits for converting between structural types. |
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. |
structural_aliases | Structural aliases for standard library types. |
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_pat | Macro to destructure the tuple returned by |
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 fields. |
path_tuple | For manually constructing a |
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_from_structural | For implementing |
z_impl_try_from_structural_for_enum | For implementing |
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
FieldCloner | Wrapper that emulates by-value access to fields by cloning them. |
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 |