Trait FnStatefulTransformerOps 

pub trait FnStatefulTransformerOps<T, R>: FnMut(T) -> R + Sized {
    // Provided methods
    fn and_then<S, F>(self, after: F) -> BoxStatefulTransformer<T, S>
       where Self: 'static,
             S: 'static,
             F: StatefulTransformer<R, S> + 'static,
             T: 'static,
             R: 'static { ... }
    fn when<P>(self, predicate: P) -> BoxConditionalStatefulTransformer<T, R>
       where Self: 'static,
             P: Predicate<T> + 'static,
             T: 'static,
             R: 'static { ... }
}

Extension trait for closures implementing FnMut(T) -> R

Provides composition methods (and_then, compose, when) for closures without requiring explicit wrapping in BoxStatefulTransformer, RcStatefulTransformer, or ArcStatefulTransformer.

This trait is automatically implemented for all closures that implement FnMut(T) -> R.

Design Rationale

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

Examples

Chain composition with and_then

use qubit_function::{StatefulTransformer, FnStatefulTransformerOps, FnTransformerOps, Transformer};

let mut counter1 = 0;
let transformer1 = move |x: i32| {
    counter1 += 1;
    x + counter1
};

let mut counter2 = 0;
let transformer2 = move |x: i32| {
    counter2 += 1;
    x * counter2
};

let mut composed = FnStatefulTransformerOps::and_then(transformer1, transformer2);
assert_eq!(composed.apply(10), 11);  // (10 + 1) * 1

Reverse composition with compose

use qubit_function::{StatefulTransformer, FnStatefulTransformerOps, FnTransformerOps, Transformer};

let transformer = |x: i32| x * 2;

let mut composed = transformer.compose(|x: i32| x + 1);
assert_eq!(composed.apply(10), 22); // (10 + 1) * 2

Conditional mapping with when

use qubit_function::{StatefulTransformer, FnStatefulTransformerOps};

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

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

Author

Haixing Hu

Provided Methods

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

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

Chain composition - applies self first, then after

Creates a new transformer that applies this transformer first, then applies the after transformer to the result. Consumes self and returns a BoxStatefulTransformer.

Type Parameters

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

Parameters

• after - The transformer to apply after self. Can be:
  • A closure: |x: R| -> S
  • A BoxStatefulTransformer<R, S>
  • An RcStatefulTransformer<R, S>
  • An ArcStatefulTransformer<R, S>
  • Any type implementing StatefulTransformer<R, S>

Returns

A new BoxStatefulTransformer<T, S> representing the composition

Examples

use qubit_function::{StatefulTransformer, FnStatefulTransformerOps, BoxStatefulTransformer};

let mut counter1 = 0;
let transformer1 = move |x: i32| {
    counter1 += 1;
    x + counter1
};

let mut counter2 = 0;
let transformer2 = BoxStatefulTransformer::new(move |x: i32| {
    counter2 += 1;
    x * counter2
});

let mut composed = transformer1.and_then(transformer2);
assert_eq!(composed.apply(10), 11);

Examples found in repository

examples/transformers/stateful_transformer_demo.rs (line 110)

fn main() {
    println!("=== StatefulTransformer Demo ===\n");

    // 1. Basic BoxStatefulTransformer with state
    println!("1. BoxStatefulTransformer with stateful counter:");
    let mut counter = 0;
    let mut mapper = BoxStatefulTransformer::new(move |x: i32| {
        counter += 1;
        format!("Item #{}: {}", counter, x)
    });

    println!("  {}", mapper.apply(100)); // Item #1: 100
    println!("  {}", mapper.apply(200)); // Item #2: 200
    println!("  {}", mapper.apply(300)); // Item #3: 300

    // 2. Composing mappers with and_then
    println!("\n2. Composing mappers with and_then:");
    let mut counter1 = 0;
    let mapper1 = BoxStatefulTransformer::new(move |x: i32| {
        counter1 += 1;
        x + counter1
    });

    let mut counter2 = 0;
    let mapper2 = BoxStatefulTransformer::new(move |x: i32| {
        counter2 += 1;
        x * counter2
    });

    let mut composed = mapper1.and_then(mapper2);
    println!("  First call:  {}", composed.apply(10)); // (10 + 1) * 1 = 11
    println!("  Second call: {}", composed.apply(10)); // (10 + 2) * 2 = 24
    println!("  Third call:  {}", composed.apply(10)); // (10 + 3) * 3 = 39

    // 3. Conditional mapping with when/or_else
    println!("\n3. Conditional mapping:");
    let mut high_count = 0;
    let mut low_count = 0;

    let mut conditional = BoxStatefulTransformer::new(move |x: i32| {
        high_count += 1;
        format!("High[{}]: {} * 2 = {}", high_count, x, x * 2)
    })
    .when(|x: &i32| *x >= 10)
    .or_else(move |x| {
        low_count += 1;
        format!("Low[{}]: {} + 1 = {}", low_count, x, x + 1)
    });

    println!("  {}", conditional.apply(15)); // High[1]: 15 * 2 = 30
    println!("  {}", conditional.apply(5)); // Low[1]: 5 + 1 = 6
    println!("  {}", conditional.apply(20)); // High[2]: 20 * 2 = 40

    // 4. RcStatefulTransformer for cloneable mappers
    println!("\n4. RcStatefulTransformer (cloneable, single-threaded):");
    let mut counter = 0;
    let mapper = RcStatefulTransformer::new(move |x: i32| {
        counter += 1;
        x + counter
    });

    let mut mapper1 = mapper.clone();
    let mut mapper2 = mapper.clone();

    println!("  mapper1: {}", mapper1.apply(10)); // 11
    println!("  mapper2: {}", mapper2.apply(10)); // 12
    println!("  mapper1: {}", mapper1.apply(10)); // 13

    // 5. ArcStatefulTransformer for thread-safe mappers
    println!("\n5. ArcStatefulTransformer (thread-safe):");
    let mut counter = 0;
    let mapper = ArcStatefulTransformer::new(move |x: i32| {
        counter += 1;
        format!("Result[{}]: {}", counter, x * 2)
    });

    let mut mapper_clone = mapper.clone();
    println!("  Original: {}", mapper_clone.apply(5)); // Result[1]: 10
    println!("  Clone:    {}", mapper_clone.apply(7)); // Result[2]: 14

    // 6. Using FnStatefulTransformerOps extension trait
    println!("\n6. Using FnStatefulTransformerOps extension trait:");
    let mut count = 0;
    let mut mapper = (move |x: i32| {
        count += 1;
        x + count
    })
    .and_then(|x| x * 2);

    println!("  {}", mapper.apply(10)); // (10 + 1) * 2 = 22
    println!("  {}", mapper.apply(10)); // (10 + 2) * 2 = 24

    // 7. Building a complex pipeline
    println!("\n7. Complex processing pipeline:");
    let mut step1_count = 0;
    let step1 = BoxStatefulTransformer::new(move |x: i32| {
        step1_count += 1;
        format!("Step1[{}]: {}", step1_count, x)
    });

    let mut step2_count = 0;
    let step2 = BoxStatefulTransformer::new(move |s: String| {
        step2_count += 1;
        format!("{} -> Step2[{}]", s, step2_count)
    });

    let mut step3_count = 0;
    let step3 = BoxStatefulTransformer::new(move |s: String| {
        step3_count += 1;
        format!("{} -> Step3[{}]", s, step3_count)
    });

    let mut pipeline = step1.and_then(step2).and_then(step3);

    println!("  {}", pipeline.apply(100));
    println!("  {}", pipeline.apply(200));

    // 7. TransformerOnce implementation - consuming transformers
    println!("\n7. TransformerOnce implementation - consuming StatefulTransformers:");

    // BoxStatefulTransformer can be consumed as TransformerOnce
    let mut counter = 0;
    let mut box_mapper = BoxStatefulTransformer::new(move |x: i32| {
        counter += 1;
        x * counter
    });
    println!(
        "  BoxStatefulTransformer consumed once: {}",
        box_mapper.apply(10)
    ); // 10 * 1 = 10

    // RcStatefulTransformer can be consumed as TransformerOnce
    let mut counter = 0;
    let mut rc_mapper = RcStatefulTransformer::new(move |x: i32| {
        counter += 1;
        x + counter
    });
    let rc_clone = rc_mapper.clone(); // Clone before consuming
    println!(
        "  RcStatefulTransformer consumed once: {}",
        rc_mapper.apply(10)
    ); // 10 + 1 = 11
    println!("  RcStatefulTransformer clone still works: {}", {
        let mut rc_clone_for_call = rc_clone.clone();
        rc_clone_for_call.apply(10)
    }); // 10 + 2 = 12

    // ArcStatefulTransformer can be consumed as TransformerOnce
    let mut counter = 0;
    let mut arc_mapper = ArcStatefulTransformer::new(move |x: i32| {
        counter += 1;
        x * counter
    });
    let arc_clone = arc_mapper.clone(); // Clone before consuming
    println!(
        "  ArcStatefulTransformer consumed once: {}",
        arc_mapper.apply(10)
    ); // 10 * 1 = 10
    println!("  ArcStatefulTransformer clone still works: {}", {
        let mut arc_clone_for_call = arc_clone.clone();
        arc_clone_for_call.apply(10)
    }); // 10 * 2 = 20

    // 8. Converting to BoxTransformerOnce
    println!("\n8. Converting StatefulTransformers to BoxTransformerOnce:");

    let mut counter = 0;
    let mapper = BoxStatefulTransformer::new(move |x: i32| {
        counter += 1;
        x * counter
    });
    let mut once_mapper = mapper.into_box();
    println!(
        "  BoxStatefulTransformer->BoxTransformerOnce: {}",
        once_mapper.apply(5)
    ); // 5 * 1 = 5

    // RcStatefulTransformer can use to_box() to preserve original
    let mut counter = 0;
    let rc_mapper = RcStatefulTransformer::new(move |x: i32| {
        counter += 1;
        x * counter
    });
    let mut once_mapper = rc_mapper.to_box();
    println!(
        "  RcStatefulTransformer->BoxTransformerOnce: {}",
        once_mapper.apply(5)
    ); // 5 * 1 = 5
    println!("  Original RcStatefulTransformer still works: {}", {
        let mut rc_original_for_call = rc_mapper.clone();
        rc_original_for_call.apply(5)
    }); // 5 * 2 = 10

    println!("\n=== Demo Complete ===");
}

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

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

Creates a conditional transformer

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

Parameters

• predicate - The condition to check. 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 BoxConditionalStatefulTransformer<T, R>

Examples

use qubit_function::{StatefulTransformer, FnStatefulTransformerOps};

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

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

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> FnStatefulTransformerOps<T, R> for F

where F: FnMut(T) -> R,

Blanket implementation of FnStatefulTransformerOps for all closures

Automatically implements FnStatefulTransformerOps<T, R> for any type that implements FnMut(T) -> R.

Author

Haixing Hu