25 unstable releases
new 0.13.3 | Mar 25, 2025 |
---|---|
0.13.1 | Oct 9, 2024 |
0.12.0 | Dec 22, 2023 |
0.10.0 | Jun 29, 2023 |
0.1.3 | May 31, 2018 |
#22 in Procedural macros
1,282,922 downloads per month
Used in 499 crates
(93 directly)
70KB
993 lines
Method delegation with less boilerplate
This crate removes some boilerplate for structs that simply delegate some of their methods to one or more of their fields.
It gives you the delegate!
macro, which delegates method calls to selected
expressions (usually inner fields).
Example:
A Stack data structure implemented using an inner Vec via delegation.
use delegate::delegate;
#[derive(Clone, Debug)]
struct Stack<T> {
inner: Vec<T>,
}
impl<T> Stack<T> {
pub fn new() -> Self <T> {
Self { inner: vec![] }
}
delegate! {
to self.inner {
pub fn is_empty(&self) -> bool;
pub fn push(&mut self, value: T);
pub fn pop(&mut self) -> Option<T>;
pub fn clear(&mut self);
#[call(len)]
pub fn size(&self) -> usize;
#[call(last)]
pub fn peek(&self) -> Option<&T>;
}
}
}
Features
Delegate to a method with a different name
struct Stack {
inner: Vec<u32>
}
impl Stack {
delegate! {
to self.inner {
#[call(push)]
pub fn add(&mut self, value: u32);
}
}
}
Use an arbitrary inner field expression
struct Wrapper {
inner: Rc<RefCell<Vec<u32>>>
}
impl Wrapper {
delegate! {
to self.inner.deref().borrow_mut() {
pub fn push(&mut self, val: u32);
}
}
}
Delegate to enum variants
use delegate::delegate;
enum Enum {
A(A),
B(B),
C { v: C },
}
struct A {
val: usize,
}
impl A {
fn dbg_inner(&self) -> usize {
dbg!(self.val);
1
}
}
struct B {
val_a: String,
}
impl B {
fn dbg_inner(&self) -> usize {
dbg!(self.val_a.clone());
2
}
}
struct C {
val_c: f64,
}
impl C {
fn dbg_inner(&self) -> usize {
dbg!(self.val_c);
3
}
}
impl Enum {
delegate! {
// transformed to
//
// ```rust
// match self {
// Enum::A(a) => a.dbg_inner(),
// Enum::B(b) => { println!("i am b"); b }.dbg_inner(),
// Enum::C { v: c } => { c }.dbg_inner(),
// }
// ```
to match self {
Enum::A(a) => a,
Enum::B(b) => { println!("i am b"); b },
Enum::C { v: c } => { c },
} {
fn dbg_inner(&self) -> usize;
}
}
}
Use modifiers that alter the generated method body
use delegate::delegate;
struct Inner;
impl Inner {
pub fn method(&self, num: u32) -> u32 { num }
pub fn method_res(&self, num: u32) -> Result<u32, ()> { Ok(num) }
}
struct Wrapper {
inner: Inner
}
impl Wrapper {
delegate! {
to self.inner {
// calls method, converts result to u64 using `From`
#[into]
pub fn method(&self, num: u32) -> u64;
// calls method, returns ()
#[call(method)]
pub fn method_noreturn(&self, num: u32);
// calls method, converts result to i6 using `TryFrom`
#[try_into]
#[call(method)]
pub fn method2(&self, num: u32) -> Result<u16, std::num::TryFromIntError>;
// calls method_res, unwraps the result
#[unwrap]
pub fn method_res(&self, num: u32) -> u32;
// calls method_res, unwraps the result, then calls into
#[unwrap]
#[into]
#[call(method_res)]
pub fn method_res_into(&self, num: u32) -> u64;
// specify explicit type for into
#[into(u64)]
#[call(method)]
pub fn method_into_explicit(&self, num: u32) -> u64;
}
}
}
Custom called expression
The #[expr()]
attribute can be used to modify the delegated call. You can use the $
sigil as a placeholder for what delegate would normally expand to, and wrap that expression with custom code.
Note: the $
placeholder isn't required and can be present multiple times if you want.
struct A(Vec<u8>);
impl A {
delegate! {
to self.0 {
#[expr(*$.unwrap())]
/// Here `$` == `self.0.get(idx)`
/// Will expand to `*self.0.get(idx).unwrap()`
fn get(&self, idx: usize) -> u8;
#[call(get)]
#[expr($?.checked_pow(2))]
/// Here `$` == `self.0.get(idx)`
/// Will expand to `self.0.get(idx)?.checked_pow(2)`
fn get_checked_pow_2(&self, idx: usize) -> Option<u8>;
}
}
}
Add additional arguments to method
struct Inner(u32);
impl Inner {
pub fn new(m: u32) -> Self {
// some "very complex" constructing work
Self(m)
}
pub fn method(&self, n: u32) -> u32 {
self.0 + n
}
}
struct Wrapper {
inner: OnceCell<Inner>,
}
impl Wrapper {
pub fn new() -> Self {
Self {
inner: OnceCell::new(),
}
}
fn content(&self, val: u32) -> &Inner {
self.inner.get_or_init(|| Inner(val))
}
delegate! {
to |k: u32| self.content(k) {
// `wrapper.method(k, num)` will call `self.content(k).method(num)`
pub fn method(&self, num: u32) -> u32;
}
}
}
Call await
on async functions
struct Inner;
impl Inner {
pub async fn method(&self, num: u32) -> u32 { num }
}
struct Wrapper {
inner: Inner
}
impl Wrapper {
delegate! {
to self.inner {
// calls method(num).await, returns impl Future<Output = u32>
pub async fn method(&self, num: u32) -> u32;
// calls method(num).await.into(), returns impl Future<Output = u64>
#[into]
#[call(method)]
pub async fn method_into(&self, num: u32) -> u64;
}
}
}
You can use the #[await(true/false)]
attribute on delegated methods to specify
if .await
should be generated after the delegated expression. It will be
generated by default if the delegated method is async
.
Delegate to multiple fields
struct MultiStack {
left: Vec<u32>,
right: Vec<u32>,
}
impl MultiStack {
delegate! {
to self.left {
/// Push an item to the top of the left stack
#[call(push)]
pub fn push_left(&mut self, value: u32);
}
to self.right {
/// Push an item to the top of the right stack
#[call(push)]
pub fn push_right(&mut self, value: u32);
}
}
}
Inline attributes
rust-delegate
inserts #[inline(always)]
automatically. You can override that decision by specifying #[inline]
manually on the delegated method.
Segment attributes
You can use an attribute on a whole delegation segment to automatically apply it to all methods in that segment:
struct Wrapper {
inner: Inner
}
impl Wrapper {
delegate! {
#[unwrap]
to self.inner {
fn foo(&self) -> u32; // calls self.inner.foo().unwrap()
fn bar(&self) -> u32; // calls self.inner.bar().unwrap()
}
}
}
Adding additional arguments
You can specify expressions in the signature that will be used as delegated arguments:
use delegate::delegate;
struct Inner;
impl Inner {
pub fn polynomial(&self, a: i32, x: i32, b: i32, y: i32, c: i32) -> i32 {
a + x * x + b * y + c
}
}
struct Wrapper {
inner: Inner,
a: i32,
b: i32,
c: i32
}
impl Wrapper {
delegate! {
to self.inner {
// Calls `polynomial` on `inner` with `self.a`, `self.b` and
// `self.c` passed as arguments `a`, `b`, and `c`, effectively
// calling `polynomial(self.a, x, self.b, y, self.c)`.
pub fn polynomial(&self, [ self.a ], x: i32, [ self.b ], y: i32, [ self.c ]) -> i32 ;
// Calls `polynomial` on `inner` with `0`s passed for arguments
// `a` and `x`, and `self.b` and `self.c` for `b` and `c`,
// effectively calling `polynomial(0, 0, self.b, y, self.c)`.
#[call(polynomial)]
pub fn linear(&self, [ 0 ], [ 0 ], [ self.b ], y: i32, [ self.c ]) -> i32 ;
}
}
}
Parameter modifiers
You can modify how will an input parameter be passed to the delegated method with parameter attribute modifiers. Currently, the following modifiers are supported:
#[into]
: Calls.into()
on the parameter passed to the delegated method.#[as_ref]
: Calls.as_ref()
on the parameter passed to the delegated method.#[newtype]
: Accesses the first tuple element (.0
) of the parameter passed to the delegated method.
Note that these modifiers might be removed in the future, try to use the more general
#[expr]
mechanism to achieve this functionality.
use delegate::delegate;
struct InnerType {}
impl InnerType {
fn foo(&self, other: Self) {}
}
impl From<Wrapper> for InnerType {
fn from(wrapper: Wrapper) -> Self {
wrapper.0
}
}
struct Wrapper(InnerType);
impl Wrapper {
delegate! {
to self.0 {
// Calls `self.0.foo(other.into());`
pub fn foo(&self, #[into] other: Self);
// Calls `self.0.bar(other.0);`
pub fn bar(&self, #[newtype] other: Self);
}
}
}
Delegate associated functions
use delegate::delegate;
struct A {}
impl A {
fn foo(a: u32) -> u32 {
a + 1
}
}
struct B;
impl B {
delegate! {
to A {
fn foo(a: u32) -> u32;
}
}
}
assert_eq!(B::foo(1), 2);
Delegate associated constants
use delegate::delegate;
trait WithConst {
const TOTO: u8;
}
struct A;
impl WithConst for A {
const TOTO: u8 = 1;
}
struct B;
impl WithConst for B {
const TOTO: u8 = 2;
}
struct C;
impl WithConst for C {
const TOTO: u8 = 2;
}
enum Enum {
A(A),
B(B),
C(C),
}
impl Enum {
delegate! {
to match self {
Self::A(a) => a,
Self::B(b) => b,
Self::C(c) => { println!("hello from c"); c },
} {
#[const(WithConst::TOTO)]
fn get_toto(&self) -> u8;
}
}
}
assert_eq!(Enum::A(A).get_toto(), <A as WithConst>::TOTO);
License
Licensed under either of
- Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
- MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)
at your option.
Contribution
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.
Conduct
Please follow the Rust Code of Conduct. For escalation or moderation issues
please contact the crate author(s) listed in Cargo.toml
.
Dependencies
~210–650KB
~15K SLoC