Struct BoxConditionalTransformer 

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

BoxConditionalTransformer struct

A conditional transformer that only executes when a predicate is satisfied. Uses BoxTransformer and BoxPredicate for single ownership semantics.

This type is typically created by calling BoxTransformer::when() and is designed to work with the or_else() method to create if-then-else logic.

Features

• Single Ownership: Not cloneable, consumes self on use
• Conditional Execution: Only transforms when predicate returns true
• Chainable: Can add or_else branch to create if-then-else logic
• Implements Transformer: Can be used anywhere a Transformer is expected

Examples

With or_else Branch

use prism3_function::{Transformer, BoxTransformer};

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

assert_eq!(conditional.apply(5), 10); // when branch executed
assert_eq!(conditional.apply(-5), 5); // or_else branch executed

Author

Haixing Hu

Implementations

impl<T, R> BoxConditionalTransformer<T, R>

where T: 'static, R: 'static,

pub fn or_else<F>(self, else_transformer: F) -> BoxTransformer<T, R>

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

Adds an else branch

Executes the original transformer when the condition is satisfied, otherwise executes else_transformer.

Parameters

• else_transformer - The transformer for the else branch, can be:
  • Closure: |x: T| -> R
  • BoxTransformer<T, R>, RcTransformer<T, R>, ArcTransformer<T, R>
  • Any type implementing Transformer<T, R>

Returns

Returns the composed BoxTransformer<T, R>

Examples

Using a closure (recommended)

use prism3_function::{Transformer, BoxTransformer};

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

assert_eq!(conditional.apply(5), 10); // Condition satisfied, execute double
assert_eq!(conditional.apply(-5), 5); // Condition not satisfied, execute negate

Examples found in repository

examples/fn_transformer_ops_demo.rs (line 56)

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 ===");
}