Crate delegate

Expand description

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).

§Features:

Delegate to a method with a different name

use delegate::delegate;

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

use delegate::delegate;

use std::rc::Rc;
use std::cell::RefCell;
use std::ops::Deref;

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>;
        }
    }
}

Call await on async functions

use delegate::delegate;

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

use delegate::delegate;

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);
        }
    }
}

Inserts #[inline(always)] automatically (unless you specify #[inline] manually on the method)
You can use an attribute on a whole segment to automatically apply it to all methods in that segment:

use delegate::delegate;

struct Inner;

impl Inner {
  fn foo(&self) -> Result<u32, ()> { Ok(0) }
  fn bar(&self) -> Result<u32, ()> { Ok(1) }
}

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()
    }
  }
}

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 ;
        }
    }
}

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]: Calls .0 on the parameter passed to the delegated method.

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);
        }
    }
}

Specify a trait through which will the delegated method be called (using UFCS.

use delegate::delegate;

struct InnerType {}
impl InnerType {
     
}

trait MyTrait {
  fn foo(&self);
}
impl MyTrait for InnerType {
  fn foo(&self) {}
}

struct Wrapper(InnerType);
impl Wrapper {
    delegate! {
        to &self.0 {
            // Calls `MyTrait::foo(&self.0)`
            #[through(MyTrait)]
            pub fn foo(&self);
        }
    }
}

Add additional arguments to method

use delegate::delegate;
use std::cell::OnceCell;
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;
        }
    }
}

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);

Macros§

delegate

Crate delegateCopy item path

§Features:

Macros§

Crate delegate