Struct BoxTransformerOnce 

pub struct BoxTransformerOnce<T, R> { /* private fields */ }

BoxTransformerOnce - consuming transformer wrapper based on Box<dyn FnOnce>

A transformer wrapper that provides single ownership with one-time use semantics. Consumes both self and the input value.

Features

• Based on: Box<dyn FnOnce(T) -> R>
• Ownership: Single ownership, cannot be cloned
• Reusability: Can only be called once (consumes self and input)
• Thread Safety: Not thread-safe (no Send + Sync requirement)

Author

Haixing Hu

Implementations

impl<T, R> BoxTransformerOnce<T, R>

pub fn new<F>(f: F) -> Self

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

Creates a new transformer.

Wraps the provided closure in the appropriate smart pointer type for this transformer implementation.

pub fn new_with_name<F>(name: &str, f: F) -> Self

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

Creates a new named transformer.

Wraps the provided closure and assigns it a name, which is useful for debugging and logging purposes.

pub fn new_with_optional_name<F>(f: F, name: Option<String>) -> Self

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

Creates a new named transformer with an optional name.

Wraps the provided closure and assigns it an optional name.

pub fn name(&self) -> Option<&str>

Gets the name of this transformer.

Returns

Returns Some(&str) if a name was set, None otherwise.

pub fn set_name(&mut self, name: &str)

Sets the name of this transformer.

Parameters

• name - The name to set for this transformer

pub fn clear_name(&mut self)

Clears the name of this transformer.

pub fn identity() -> BoxTransformerOnce<T, T>

Creates an identity transformer.

Creates a transformer that returns the input value unchanged. Useful for default values or placeholder implementations.

Returns

Returns a new transformer instance that returns the input unchanged.

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

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

Creates a conditional transformer that executes based on predicate result.

Parameters

• predicate - The predicate to determine whether to execute the transformation operation

Returns

Returns a conditional transformer that only executes when the predicate returns true.

Examples

use std::sync::Arc;
use std::sync::atomic::{AtomicI32, Ordering};
use qubit_function::transformers::*;

let transformer = BoxTransformer::new({
    |value: i32| value * 2
});

let conditional = transformer.when(|value: &i32| *value > 0).or_else(|value: i32| value);
assert_eq!(conditional.apply(5), 10);  // transformed
assert_eq!(conditional.apply(-1), -1); // identity (unchanged)

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

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

Chains execution with another transformer, executing the current transformer first, then the subsequent transformer.

Parameters

• after - The subsequent transformer to execute after the current transformer completes

Returns

Returns a new transformer that executes the current transformer and the subsequent transformer in sequence.

Examples

use qubit_function::transformers::*;

let transformer1 = BoxTransformer::new({
    |value: i32| value + 1
});

let transformer2 = BoxTransformer::new({
    |value: i32| value * 2
});

let chained = transformer1.and_then(transformer2);
assert_eq!(chained.apply(5), 12); // (5 + 1) * 2 = 12

Examples found in repository

examples/transformers/fn_transformer_once_ops_demo.rs (line 38)

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

    // 1. Basic and_then composition
    println!("1. Basic and_then composition:");
    let parse = |s: String| s.parse::<i32>().unwrap_or(0);
    let double = |x: i32| x * 2;
    let composed = parse.and_then(double);
    println!(
        "   parse.and_then(double).apply(\"21\") = {}",
        composed.apply("21".to_string())
    );
    println!();

    // 2. Chained and_then composition
    println!("2. Chained and_then composition:");
    let parse = |s: String| s.parse::<i32>().unwrap_or(0);
    let add_one = |x: i32| x + 1;
    let double = |x: i32| x * 2;
    let chained = parse.and_then(add_one).and_then(double);
    println!(
        "   parse.and_then(add_one).and_then(double).apply(\"5\") = {}",
        chained.apply("5".to_string())
    ); // (5 + 1) * 2 = 12
    println!();

    // 3. More and_then composition
    println!("3. More 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)
    ); // (21 * 2).to_string() = "42"
    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

    let double2 = |x: i32| x * 2;
    let conditional2 = double2.when(|x: &i32| *x > 0).or_else(|x: i32| -x);
    println!("     transform(-5) = {}", conditional2.apply(-5)); // 5
    println!();

    // 5. Complex composition
    println!("5. Complex composition:");
    let parse = |s: String| s.parse::<i32>().unwrap_or(0);
    let double = |x: i32| x * 2;
    let triple = |x: i32| x * 3;
    let to_string = |x: i32| x.to_string();

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

    println!("   parse.and_then(double.when(x > 5).or_else(triple)).and_then(to_string):");
    println!("     transform(\"3\") = {}", complex.apply("3".to_string())); // 3 <= 5, so 3 * 3 = 9

    let parse2 = |s: String| s.parse::<i32>().unwrap_or(0);
    let double2 = |x: i32| x * 2;
    let triple2 = |x: i32| x * 3;
    let to_string2 = |x: i32| x.to_string();
    let complex2 = parse2
        .and_then(double2.when(|x: &i32| *x > 5).or_else(triple2))
        .and_then(to_string2);
    println!(
        "     transform(\"10\") = {}",
        complex2.apply("10".to_string())
    ); // 10 > 5, so 10 * 2 = 20
    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 parse_fn(s: String) -> i32 {
        s.parse().unwrap_or(0)
    }
    fn double_fn(x: i32) -> i32 {
        x * 2
    }
    let fn_composed = parse_fn.and_then(double_fn);
    println!(
        "   parse_fn.and_then(double_fn).apply(\"21\") = {}",
        fn_composed.apply("21".to_string())
    ); // 42
    println!();

    // 9. String operations that consume ownership
    println!("9. String operations that consume ownership:");
    let owned = String::from("hello");
    let append = move |s: String| format!("{} {}", s, owned);
    let uppercase = |s: String| s.to_uppercase();
    let composed = append.and_then(uppercase);
    println!(
        "   append.and_then(uppercase).apply(\"world\") = {}",
        composed.apply("world".to_string())
    ); // "WORLD HELLO"
    println!();

    // 10. Parsing and validation
    println!("10. Parsing and validation:");
    let parse = |s: String| s.parse::<i32>().unwrap_or(0);
    let validate = |x: i32| if x > 0 { x } else { 1 };
    let composed = parse.and_then(validate);
    println!(
        "   parse.and_then(validate).apply(\"42\") = {}",
        composed.apply("42".to_string())
    ); // 42

    let parse2 = |s: String| s.parse::<i32>().unwrap_or(0);
    let validate2 = |x: i32| if x > 0 { x } else { 1 };
    let composed2 = parse2.and_then(validate2);
    println!(
        "   parse.and_then(validate).apply(\"-5\") = {}",
        composed2.apply("-5".to_string())
    ); // 1
    println!();

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

impl<T, R> BoxTransformerOnce<T, R>

pub fn constant(value: R) -> BoxTransformerOnce<T, R>

where R: Clone + 'static,

Creates a constant transformer

Examples

/// rust /// use qubit_function::{BoxTransformerOnce, Transformer}; /// /// let constant = BoxTransformerOnce::constant("hello"); /// assert_eq!(constant.apply(123), "hello"); ///

Trait Implementations

impl<T, R> Debug for BoxTransformerOnce<T, R>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<T, R> Display for BoxTransformerOnce<T, R>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<T, R> TransformerOnce<T, R> for BoxTransformerOnce<T, R>

fn apply(self, input: T) -> R

Transforms the input value, consuming both self and input

fn into_box(self) -> BoxTransformerOnce<T, R>

Converts to BoxTransformerOnce

fn into_fn(self) -> impl FnOnce(T) -> R

Converts transformer to a closure