Trait FnTransformerOps 

pub trait FnTransformerOps<T, R>: Fn(T) -> R + Sized {
    // Provided methods
    fn and_then<S, F>(self, after: F) -> BoxTransformer<T, S>
       where Self: 'static,
             S: 'static,
             F: Transformer<R, S> + 'static,
             T: 'static,
             R: 'static { ... }
    fn compose<S, F>(self, before: F) -> BoxTransformer<S, R>
       where Self: 'static,
             S: 'static,
             F: Transformer<S, T> + 'static,
             T: 'static,
             R: 'static { ... }
    fn when<P>(self, predicate: P) -> BoxConditionalTransformer<T, R>
       where Self: 'static,
             P: Predicate<T> + 'static,
             T: 'static,
             R: 'static { ... }
}

Extension trait for closures implementing the base transformer trait

Provides composition methods (and_then, compose, 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 transformer trait.

Design Rationale

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

Provided Methods

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

where Self: 'static, S: 'static, F: Transformer<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 Box-based transformer.

Type Parameters

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

Parameters

• after - The transformer to apply after self. Note: This parameter is passed by value and will transfer ownership. If you need to preserve the original transformer, clone it first (if it implements Clone). Can be:
  • A closure
  • A function pointer
  • A Box-based transformer
  • An Rc-based transformer
  • An Arc-based transformer
  • Any type implementing the transformer trait

Returns

A new Box-based transformer representing the composition

Examples

Direct value passing (ownership transfer)

use qubit_function::{BoxTransformer, FnTransformerOps, Transformer};

let double = |x: i32| x * 2;
let to_string = BoxTransformer::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 behavior with separate closures

use qubit_function::{BoxTransformer, FnTransformerOps, Transformer};

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

let composed = double.and_then(BoxTransformer::new(|x: i32| x.to_string()));
assert_eq!(composed.apply(21), "42");

assert_eq!(to_string_for_validation(5), "5");

Examples found in repository

examples/transformers/fn_transformer_ops_demo.rs (line 27)

fn main() {
    println!("=== FnTransformerOps Example ===\n");

    // 1. Basic and_then composition
    println!("1. Basic and_then composition:");
    let double = |x: i32| x * 2;
    let to_string = |x: i32| x.to_string();
    let composed = double.and_then(to_string);
    println!("   double.and_then(to_string).apply(21) = {}", composed.apply(21));
    println!();

    // 2. Chained and_then composition
    println!("2. Chained and_then composition:");
    let add_one = |x: i32| x + 1;
    let double = |x: i32| x * 2;
    let to_string = |x: i32| x.to_string();
    let chained = add_one.and_then(double).and_then(to_string);
    println!(
        "   add_one.and_then(double).and_then(to_string).apply(5) = {}",
        chained.apply(5)
    ); // (5 + 1) * 2 = 12
    println!();

    // 3. compose reverse composition
    println!("3. compose reverse composition:");
    let double = |x: i32| x * 2;
    let add_one = |x: i32| x + 1;
    let composed = double.compose(add_one);
    println!("   double.compose(add_one).apply(5) = {}", composed.apply(5)); // (5 + 1) * 2 = 12
    println!();

    // 4. Conditional transformation when
    println!("4. Conditional transformation when:");
    let double = |x: i32| x * 2;
    let conditional = double.when(|x: &i32| *x > 0).or_else(|x: i32| -x);
    println!("   double.when(x > 0).or_else(negate):");
    println!("     transform(5) = {}", conditional.apply(5)); // 10
    println!("     transform(-5) = {}", conditional.apply(-5)); // 5
    println!();

    // 5. Complex composition
    println!("5. Complex composition:");
    let add_one = |x: i32| x + 1;
    let double = |x: i32| x * 2;
    let triple = |x: i32| x * 3;
    let to_string = |x: i32| x.to_string();

    let complex = add_one
        .and_then(double.when(|x: &i32| *x > 5).or_else(triple))
        .and_then(to_string);

    println!("   add_one.and_then(double.when(x > 5).or_else(triple)).and_then(to_string):");
    println!("     transform(1) = {}", complex.apply(1)); // (1 + 1) = 2 <= 5, so 2 * 3 = 6
    println!("     transform(5) = {}", complex.apply(5)); // (5 + 1) = 6 > 5, so 6 * 2 = 12
    println!("     transform(10) = {}", complex.apply(10)); // (10 + 1) = 11 > 5, so 11 * 2 = 22
    println!();

    // 6. Type conversion
    println!("6. Type conversion:");
    let to_string = |x: i32| x.to_string();
    let get_length = |s: String| s.len();
    let length_transformer = to_string.and_then(get_length);
    println!(
        "   to_string.and_then(get_length).apply(12345) = {}",
        length_transformer.apply(12345)
    ); // 5
    println!();

    // 7. Closures that capture environment
    println!("7. Closures that capture environment:");
    let multiplier = 3;
    let multiply = move |x: i32| x * multiplier;
    let add_ten = |x: i32| x + 10;
    let with_capture = multiply.and_then(add_ten);
    println!("   multiply(3).and_then(add_ten).apply(5) = {}", with_capture.apply(5)); // 5 * 3 + 10 = 25
    println!();

    // 8. Function pointers
    println!("8. Function pointers:");
    fn double_fn(x: i32) -> i32 {
        x * 2
    }
    fn add_one_fn(x: i32) -> i32 {
        x + 1
    }
    let fn_composed = double_fn.and_then(add_one_fn);
    println!("   double_fn.and_then(add_one_fn).apply(5) = {}", fn_composed.apply(5)); // 5 * 2 + 1 = 11
    println!();

    // 9. Multi-conditional transformation
    println!("9. Multi-conditional transformation:");
    let abs = |x: i32| x.abs();
    let double = |x: i32| x * 2;
    let transformer = abs.when(|x: &i32| *x < 0).or_else(double);
    println!("   abs.when(x < 0).or_else(double):");
    println!("     transform(-5) = {}", transformer.apply(-5)); // abs(-5) = 5
    println!("     transform(5) = {}", transformer.apply(5)); // 5 * 2 = 10
    println!("     transform(0) = {}", transformer.apply(0)); // 0 * 2 = 0
    println!();

    println!("=== Example completed ===");
}

fn compose<S, F>(self, before: F) -> BoxTransformer<S, R>

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

Reverse composition - applies before first, then self.

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

Type Parameters

• S - The input type of the before transformer
• F - The type of the before transformer

Parameters

• before - The transformer to apply before self.

Returns

A new Box-based transformer representing the reverse composition.

Examples found in repository

examples/transformers/fn_transformer_ops_demo.rs (line 47)

fn main() {
    println!("=== FnTransformerOps Example ===\n");

    // 1. Basic and_then composition
    println!("1. Basic and_then composition:");
    let double = |x: i32| x * 2;
    let to_string = |x: i32| x.to_string();
    let composed = double.and_then(to_string);
    println!("   double.and_then(to_string).apply(21) = {}", composed.apply(21));
    println!();

    // 2. Chained and_then composition
    println!("2. Chained and_then composition:");
    let add_one = |x: i32| x + 1;
    let double = |x: i32| x * 2;
    let to_string = |x: i32| x.to_string();
    let chained = add_one.and_then(double).and_then(to_string);
    println!(
        "   add_one.and_then(double).and_then(to_string).apply(5) = {}",
        chained.apply(5)
    ); // (5 + 1) * 2 = 12
    println!();

    // 3. compose reverse composition
    println!("3. compose reverse composition:");
    let double = |x: i32| x * 2;
    let add_one = |x: i32| x + 1;
    let composed = double.compose(add_one);
    println!("   double.compose(add_one).apply(5) = {}", composed.apply(5)); // (5 + 1) * 2 = 12
    println!();

    // 4. Conditional transformation when
    println!("4. Conditional transformation when:");
    let double = |x: i32| x * 2;
    let conditional = double.when(|x: &i32| *x > 0).or_else(|x: i32| -x);
    println!("   double.when(x > 0).or_else(negate):");
    println!("     transform(5) = {}", conditional.apply(5)); // 10
    println!("     transform(-5) = {}", conditional.apply(-5)); // 5
    println!();

    // 5. Complex composition
    println!("5. Complex composition:");
    let add_one = |x: i32| x + 1;
    let double = |x: i32| x * 2;
    let triple = |x: i32| x * 3;
    let to_string = |x: i32| x.to_string();

    let complex = add_one
        .and_then(double.when(|x: &i32| *x > 5).or_else(triple))
        .and_then(to_string);

    println!("   add_one.and_then(double.when(x > 5).or_else(triple)).and_then(to_string):");
    println!("     transform(1) = {}", complex.apply(1)); // (1 + 1) = 2 <= 5, so 2 * 3 = 6
    println!("     transform(5) = {}", complex.apply(5)); // (5 + 1) = 6 > 5, so 6 * 2 = 12
    println!("     transform(10) = {}", complex.apply(10)); // (10 + 1) = 11 > 5, so 11 * 2 = 22
    println!();

    // 6. Type conversion
    println!("6. Type conversion:");
    let to_string = |x: i32| x.to_string();
    let get_length = |s: String| s.len();
    let length_transformer = to_string.and_then(get_length);
    println!(
        "   to_string.and_then(get_length).apply(12345) = {}",
        length_transformer.apply(12345)
    ); // 5
    println!();

    // 7. Closures that capture environment
    println!("7. Closures that capture environment:");
    let multiplier = 3;
    let multiply = move |x: i32| x * multiplier;
    let add_ten = |x: i32| x + 10;
    let with_capture = multiply.and_then(add_ten);
    println!("   multiply(3).and_then(add_ten).apply(5) = {}", with_capture.apply(5)); // 5 * 3 + 10 = 25
    println!();

    // 8. Function pointers
    println!("8. Function pointers:");
    fn double_fn(x: i32) -> i32 {
        x * 2
    }
    fn add_one_fn(x: i32) -> i32 {
        x + 1
    }
    let fn_composed = double_fn.and_then(add_one_fn);
    println!("   double_fn.and_then(add_one_fn).apply(5) = {}", fn_composed.apply(5)); // 5 * 2 + 1 = 11
    println!();

    // 9. Multi-conditional transformation
    println!("9. Multi-conditional transformation:");
    let abs = |x: i32| x.abs();
    let double = |x: i32| x * 2;
    let transformer = abs.when(|x: &i32| *x < 0).or_else(double);
    println!("   abs.when(x < 0).or_else(double):");
    println!("     transform(-5) = {}", transformer.apply(-5)); // abs(-5) = 5
    println!("     transform(5) = {}", transformer.apply(5)); // 5 * 2 = 10
    println!("     transform(0) = {}", transformer.apply(0)); // 0 * 2 = 0
    println!();

    println!("=== Example completed ===");
}

fn when<P>(self, predicate: P) -> BoxConditionalTransformer<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. 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 transformer type

Examples

Basic usage with or_else

use qubit_function::{Transformer, FnTransformerOps};

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);

Reusing equivalent predicate logic

use qubit_function::{FnTransformerOps, Transformer};

let double = |x: i32| x * 2;
let is_positive_for_validation = |x: &i32| *x > 0;

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

assert_eq!(conditional.apply(5), 10);
assert!(is_positive_for_validation(&3));

Examples found in repository

examples/transformers/fn_transformer_ops_demo.rs (line 54)

fn main() {
    println!("=== FnTransformerOps Example ===\n");

    // 1. Basic and_then composition
    println!("1. Basic and_then composition:");
    let double = |x: i32| x * 2;
    let to_string = |x: i32| x.to_string();
    let composed = double.and_then(to_string);
    println!("   double.and_then(to_string).apply(21) = {}", composed.apply(21));
    println!();

    // 2. Chained and_then composition
    println!("2. Chained and_then composition:");
    let add_one = |x: i32| x + 1;
    let double = |x: i32| x * 2;
    let to_string = |x: i32| x.to_string();
    let chained = add_one.and_then(double).and_then(to_string);
    println!(
        "   add_one.and_then(double).and_then(to_string).apply(5) = {}",
        chained.apply(5)
    ); // (5 + 1) * 2 = 12
    println!();

    // 3. compose reverse composition
    println!("3. compose reverse composition:");
    let double = |x: i32| x * 2;
    let add_one = |x: i32| x + 1;
    let composed = double.compose(add_one);
    println!("   double.compose(add_one).apply(5) = {}", composed.apply(5)); // (5 + 1) * 2 = 12
    println!();

    // 4. Conditional transformation when
    println!("4. Conditional transformation when:");
    let double = |x: i32| x * 2;
    let conditional = double.when(|x: &i32| *x > 0).or_else(|x: i32| -x);
    println!("   double.when(x > 0).or_else(negate):");
    println!("     transform(5) = {}", conditional.apply(5)); // 10
    println!("     transform(-5) = {}", conditional.apply(-5)); // 5
    println!();

    // 5. Complex composition
    println!("5. Complex composition:");
    let add_one = |x: i32| x + 1;
    let double = |x: i32| x * 2;
    let triple = |x: i32| x * 3;
    let to_string = |x: i32| x.to_string();

    let complex = add_one
        .and_then(double.when(|x: &i32| *x > 5).or_else(triple))
        .and_then(to_string);

    println!("   add_one.and_then(double.when(x > 5).or_else(triple)).and_then(to_string):");
    println!("     transform(1) = {}", complex.apply(1)); // (1 + 1) = 2 <= 5, so 2 * 3 = 6
    println!("     transform(5) = {}", complex.apply(5)); // (5 + 1) = 6 > 5, so 6 * 2 = 12
    println!("     transform(10) = {}", complex.apply(10)); // (10 + 1) = 11 > 5, so 11 * 2 = 22
    println!();

    // 6. Type conversion
    println!("6. Type conversion:");
    let to_string = |x: i32| x.to_string();
    let get_length = |s: String| s.len();
    let length_transformer = to_string.and_then(get_length);
    println!(
        "   to_string.and_then(get_length).apply(12345) = {}",
        length_transformer.apply(12345)
    ); // 5
    println!();

    // 7. Closures that capture environment
    println!("7. Closures that capture environment:");
    let multiplier = 3;
    let multiply = move |x: i32| x * multiplier;
    let add_ten = |x: i32| x + 10;
    let with_capture = multiply.and_then(add_ten);
    println!("   multiply(3).and_then(add_ten).apply(5) = {}", with_capture.apply(5)); // 5 * 3 + 10 = 25
    println!();

    // 8. Function pointers
    println!("8. Function pointers:");
    fn double_fn(x: i32) -> i32 {
        x * 2
    }
    fn add_one_fn(x: i32) -> i32 {
        x + 1
    }
    let fn_composed = double_fn.and_then(add_one_fn);
    println!("   double_fn.and_then(add_one_fn).apply(5) = {}", fn_composed.apply(5)); // 5 * 2 + 1 = 11
    println!();

    // 9. Multi-conditional transformation
    println!("9. Multi-conditional transformation:");
    let abs = |x: i32| x.abs();
    let double = |x: i32| x * 2;
    let transformer = abs.when(|x: &i32| *x < 0).or_else(double);
    println!("   abs.when(x < 0).or_else(double):");
    println!("     transform(-5) = {}", transformer.apply(-5)); // abs(-5) = 5
    println!("     transform(5) = {}", transformer.apply(5)); // 5 * 2 = 10
    println!("     transform(0) = {}", transformer.apply(0)); // 0 * 2 = 0
    println!();

    println!("=== Example completed ===");
}

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementors

impl<T, R, F> FnTransformerOps<T, R> for F

where F: Fn(T) -> R,

Blanket implementation for all closures

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