Trait FnStatefulFunctionOps 

pub trait FnStatefulFunctionOps<T, R>:
    FnMut(&T) -> R
    + Sized
    + 'static {
    // Provided methods
    fn and_then<S, F>(self, after: F) -> BoxStatefulFunction<T, S>
       where S: 'static,
             F: StatefulFunction<R, S> + 'static,
             T: 'static,
             R: 'static { ... }
    fn when<P>(self, predicate: P) -> BoxConditionalStatefulFunction<T, R>
       where P: Predicate<T> + 'static,
             T: 'static,
             R: 'static { ... }
}

Extension trait for closures implementing the base function trait

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

This trait is automatically implemented for all closures and function pointers that implement the base function trait.

Design Rationale

While closures automatically implement the base function trait through blanket implementation, they don’t have access to instance methods like and_then, and when. This extension trait provides those methods, returning the appropriate Box-based function type for maximum flexibility.

Examples

Chain composition with and_then

use prism3_function::{Function, FnFunctionOps};

let double = |x: i32| x * 2;
let to_string = |x: i32| x.to_string();

let composed = double.and_then(to_string);
assert_eq!(composed.apply(21), "42");

Conditional transformation with when

use prism3_function::{Function, FnFunctionOps};

let double = |x: i32| x * 2;
let conditional = double.when(|x: &i32| *x > 0).or_else(|x: i32| -x);

assert_eq!(conditional.apply(5), 10);
assert_eq!(conditional.apply(-5), 5);

Author

Haixing Hu

Provided Methods

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

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

Chain composition - applies self first, then after

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

Type Parameters

• S - The output type of the after function
• F - The type of the after function (must implement the function trait)

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
  • A function pointer
  • A Box-based function
  • An Rc-based function
  • An Arc-based function
  • Any type implementing the function trait

Returns

A new Box-based function representing the composition

Examples

Direct value passing (ownership transfer)

use prism3_function::{Function, FnFunctionOps, BoxFunction};

let double = |x: i32| x * 2;
let to_string = BoxFunction::new(|x: i32| x.to_string());

// to_string is moved here
let composed = double.and_then(to_string);
assert_eq!(composed.apply(21), "42");
// to_string.apply(5); // Would not compile - moved

Preserving original with clone

use prism3_function::{Function, FnFunctionOps, BoxFunction};

let double = |x: i32| x * 2;
let to_string = BoxFunction::new(|x: i32| x.to_string());

// Clone to preserve original
let composed = double.and_then(to_string.clone());
assert_eq!(composed.apply(21), "42");

// Original still usable
assert_eq!(to_string.apply(5), "5");

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

where P: Predicate<T> + 'static, T: 'static, R: 'static,

Creates a conditional function

Returns a function that only executes when a predicate is satisfied. You must call or_else() to provide an alternative 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 predicate, clone it first (if it implements Clone). Can be:
  • A closure: |x: &T| -> bool
  • A function pointer: fn(&T) -> bool
  • A BoxPredicate<T>
  • An RcPredicate<T>
  • An ArcPredicate<T>
  • Any type implementing Predicate<T>

Returns

Returns the appropriate conditional function type

Examples

Basic usage with or_else

use prism3_function::{Function, FnFunctionOps};

let double = |x: i32| x * 2;
let conditional = double.when(|x: &i32| *x > 0).or_else(|x: i32| -x);

assert_eq!(conditional.apply(5), 10);
assert_eq!(conditional.apply(-5), 5);

Preserving predicate with clone

use prism3_function::{Function, FnFunctionOps, BoxPredicate};

let double = |x: i32| x * 2;
let is_positive = BoxPredicate::new(|x: &i32| *x > 0);

// Clone to preserve original predicate
let conditional = double.when(is_positive.clone())
    .or_else(|x: i32| -x);

assert_eq!(conditional.apply(5), 10);

// Original predicate still usable
assert!(is_positive.test(&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, R, F> FnStatefulFunctionOps<T, R> for F

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

Blanket implementation for all closures

Automatically implements the extension trait for any type that implements the base function trait.

Author

Haixing Hu