Trait FnBiFunctionOps 

pub trait FnBiFunctionOps<T, U, R>:
    Fn(&T, &U) -> R
    + Sized
    + 'static {
    // Provided methods
    fn and_then<S, F>(self, after: F) -> BoxBiFunction<T, U, S>
       where S: 'static,
             F: Function<R, S> + 'static,
             T: 'static,
             U: 'static,
             R: 'static { ... }
    fn when<P>(self, predicate: P) -> BoxConditionalBiFunction<T, U, R>
       where P: BiPredicate<T, U> + 'static,
             T: 'static,
             U: 'static,
             R: 'static { ... }
}

Extension trait for closures implementing Fn(&T, &U) -> R

Provides composition methods (and_then, when) for bi-function closures and function pointers without requiring explicit wrapping in BoxBiFunction.

This trait is automatically implemented for all closures and function pointers that implement Fn(&T, &U) -> R.

Design Rationale

While closures automatically implement BiFunction<T, U, R> through blanket implementation, they don’t have access to instance methods like and_then and when. This extension trait provides those methods, returning BoxBiFunction for maximum flexibility.

Examples

Chain composition with and_then

use prism3_function::{BiFunction, FnBiFunctionOps};

let add = |x: &i32, y: &i32| *x + *y;
let double = |x: i32| x * 2;

let composed = add.and_then(double);
assert_eq!(composed.apply(&3, &5), 16); // (3 + 5) * 2

Conditional execution with when

use prism3_function::{BiFunction, FnBiFunctionOps};

let add = |x: &i32, y: &i32| *x + *y;
let multiply = |x: &i32, y: &i32| *x * *y;

let conditional = add.when(|x: &i32, y: &i32| *x > 0 && *y > 0).or_else(multiply);

assert_eq!(conditional.apply(&5, &3), 8);   // add
assert_eq!(conditional.apply(&-5, &3), -15); // multiply

Author

Haixing Hu

Provided Methods

fn and_then<S, F>(self, after: F) -> BoxBiFunction<T, U, S>

where S: 'static, F: Function<R, S> + 'static, T: 'static, U: 'static, R: 'static,

Chain composition - applies self first, then after

Creates a new bi-function that applies this bi-function first, then applies the after function to the result. Consumes self and returns a BoxBiFunction.

Type Parameters

• S - The output type of the after function
• F - The type of the after function (must implement Function<R, S>)

Parameters

• after - The function to apply after self. Note: This parameter is passed by value and will transfer ownership. If you need to preserve the original function, clone it first (if it implements Clone). Can be:
  • A closure: |x: R| -> S
  • A function pointer: fn(R) -> S
  • A BoxFunction<R, S>
  • An RcFunction<R, S>
  • An ArcFunction<R, S>
  • Any type implementing Function<R, S>

Returns

A new BoxBiFunction<T, U, S> representing the composition

Examples

Direct value passing (ownership transfer)

use prism3_function::{BiFunction, FnBiFunctionOps,
    BoxFunction};

let add = |x: &i32, y: &i32| *x + *y;
let to_string = BoxFunction::new(|x: i32| x.to_string());

// to_string is moved here
let composed = add.and_then(to_string);
assert_eq!(composed.apply(&20, &22), "42");
// to_string.apply(10); // Would not compile - moved

Preserving original with clone

use prism3_function::{BiFunction, FnBiFunctionOps,
    BoxFunction};

let add = |x: &i32, y: &i32| *x + *y;
let to_string = BoxFunction::new(|x: i32| x.to_string());

// Clone to preserve original
let composed = add.and_then(to_string.clone());
assert_eq!(composed.apply(&20, &22), "42");

// Original still usable
assert_eq!(to_string.apply(&10), "10");

fn when<P>(self, predicate: P) -> BoxConditionalBiFunction<T, U, R>

where P: BiPredicate<T, U> + 'static, T: 'static, U: 'static, R: 'static,

Creates a conditional bi-function

Returns a bi-function that only executes when a bi-predicate is satisfied. You must call or_else() to provide an alternative bi-function for when the condition is not satisfied.

Parameters

• predicate - The condition to check. Note: This parameter is passed by value and will transfer ownership. If you need to preserve the original bi-predicate, clone it first (if it implements Clone). Can be:
  • A closure: |x: &T, y: &U| -> bool
  • A function pointer: fn(&T, &U) -> bool
  • A BoxBiPredicate<T, U>
  • An RcBiPredicate<T, U>
  • An ArcBiPredicate<T, U>
  • Any type implementing BiPredicate<T, U>

Returns

Returns BoxConditionalBiFunction<T, U, R>

Examples

Basic usage with or_else

use prism3_function::{BiFunction, FnBiFunctionOps};

let add = |x: &i32, y: &i32| *x + *y;
let conditional = add.when(|x: &i32, y: &i32| *x > 0)
    .or_else(|x: &i32, y: &i32| *x * *y);

assert_eq!(conditional.apply(&5, &3), 8);
assert_eq!(conditional.apply(&-5, &3), -15);

Preserving bi-predicate with clone

use prism3_function::{BiFunction, FnBiFunctionOps,
    RcBiPredicate};

let add = |x: &i32, y: &i32| *x + *y;
let both_positive = RcBiPredicate::new(|x: &i32, y: &i32|
    *x > 0 && *y > 0);

// Clone to preserve original bi-predicate
let conditional = add.when(both_positive.clone())
    .or_else(|x: &i32, y: &i32| *x * *y);

assert_eq!(conditional.apply(&5, &3), 8);

// Original bi-predicate still usable
assert!(both_positive.test(&5, &3));

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Implementors

impl<T, U, R, F> FnBiFunctionOps<T, U, R> for F

where F: Fn(&T, &U) -> R + 'static,

Blanket implementation of FnBiFunctionOps for all closures

Automatically implements FnBiFunctionOps<T, U, R> for any type that implements Fn(&T, &U) -> R.

Author

Haixing Hu