fn_transformer_ops_demo/
fn_transformer_ops_demo.rs

1/*******************************************************************************
2 *
3 *    Copyright (c) 2025 - 2026 Haixing Hu.
4 *
5 *    SPDX-License-Identifier: Apache-2.0
6 *
7 *    Licensed under the Apache License, Version 2.0.
8 *
9 ******************************************************************************/
10//! Demonstrates the usage of FnTransformerOps extension trait
11//!
12//! This example shows how to directly use and_then, compose, and when methods on closures,
13//! without explicitly wrapping them in BoxTransformer, RcTransformer, or ArcTransformer.
14
15use qubit_function::{
16    FnTransformerOps,
17    Transformer,
18};
19
20fn main() {
21    println!("=== FnTransformerOps Example ===\n");
22
23    // 1. Basic and_then composition
24    println!("1. Basic and_then composition:");
25    let double = |x: i32| x * 2;
26    let to_string = |x: i32| x.to_string();
27    let composed = double.and_then(to_string);
28    println!("   double.and_then(to_string).apply(21) = {}", composed.apply(21));
29    println!();
30
31    // 2. Chained and_then composition
32    println!("2. Chained and_then composition:");
33    let add_one = |x: i32| x + 1;
34    let double = |x: i32| x * 2;
35    let to_string = |x: i32| x.to_string();
36    let chained = add_one.and_then(double).and_then(to_string);
37    println!(
38        "   add_one.and_then(double).and_then(to_string).apply(5) = {}",
39        chained.apply(5)
40    ); // (5 + 1) * 2 = 12
41    println!();
42
43    // 3. compose reverse composition
44    println!("3. compose reverse composition:");
45    let double = |x: i32| x * 2;
46    let add_one = |x: i32| x + 1;
47    let composed = double.compose(add_one);
48    println!("   double.compose(add_one).apply(5) = {}", composed.apply(5)); // (5 + 1) * 2 = 12
49    println!();
50
51    // 4. Conditional transformation when
52    println!("4. Conditional transformation when:");
53    let double = |x: i32| x * 2;
54    let conditional = double.when(|x: &i32| *x > 0).or_else(|x: i32| -x);
55    println!("   double.when(x > 0).or_else(negate):");
56    println!("     transform(5) = {}", conditional.apply(5)); // 10
57    println!("     transform(-5) = {}", conditional.apply(-5)); // 5
58    println!();
59
60    // 5. Complex composition
61    println!("5. Complex composition:");
62    let add_one = |x: i32| x + 1;
63    let double = |x: i32| x * 2;
64    let triple = |x: i32| x * 3;
65    let to_string = |x: i32| x.to_string();
66
67    let complex = add_one
68        .and_then(double.when(|x: &i32| *x > 5).or_else(triple))
69        .and_then(to_string);
70
71    println!("   add_one.and_then(double.when(x > 5).or_else(triple)).and_then(to_string):");
72    println!("     transform(1) = {}", complex.apply(1)); // (1 + 1) = 2 <= 5, so 2 * 3 = 6
73    println!("     transform(5) = {}", complex.apply(5)); // (5 + 1) = 6 > 5, so 6 * 2 = 12
74    println!("     transform(10) = {}", complex.apply(10)); // (10 + 1) = 11 > 5, so 11 * 2 = 22
75    println!();
76
77    // 6. Type conversion
78    println!("6. Type conversion:");
79    let to_string = |x: i32| x.to_string();
80    let get_length = |s: String| s.len();
81    let length_transformer = to_string.and_then(get_length);
82    println!(
83        "   to_string.and_then(get_length).apply(12345) = {}",
84        length_transformer.apply(12345)
85    ); // 5
86    println!();
87
88    // 7. Closures that capture environment
89    println!("7. Closures that capture environment:");
90    let multiplier = 3;
91    let multiply = move |x: i32| x * multiplier;
92    let add_ten = |x: i32| x + 10;
93    let with_capture = multiply.and_then(add_ten);
94    println!("   multiply(3).and_then(add_ten).apply(5) = {}", with_capture.apply(5)); // 5 * 3 + 10 = 25
95    println!();
96
97    // 8. Function pointers
98    println!("8. Function pointers:");
99    fn double_fn(x: i32) -> i32 {
100        x * 2
101    }
102    fn add_one_fn(x: i32) -> i32 {
103        x + 1
104    }
105    let fn_composed = double_fn.and_then(add_one_fn);
106    println!("   double_fn.and_then(add_one_fn).apply(5) = {}", fn_composed.apply(5)); // 5 * 2 + 1 = 11
107    println!();
108
109    // 9. Multi-conditional transformation
110    println!("9. Multi-conditional transformation:");
111    let abs = |x: i32| x.abs();
112    let double = |x: i32| x * 2;
113    let transformer = abs.when(|x: &i32| *x < 0).or_else(double);
114    println!("   abs.when(x < 0).or_else(double):");
115    println!("     transform(-5) = {}", transformer.apply(-5)); // abs(-5) = 5
116    println!("     transform(5) = {}", transformer.apply(5)); // 5 * 2 = 10
117    println!("     transform(0) = {}", transformer.apply(0)); // 0 * 2 = 0
118    println!();
119
120    println!("=== Example completed ===");
121}
fn_transformer_ops_demo/fn_transformer_ops_demo.rs

fn_transformer_ops_demo/
fn_transformer_ops_demo.rs
