72 lines
1.5 KiB
Rust
72 lines
1.5 KiB
Rust
// motivation for closures
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fn sum<T: std::ops::AddAssign + Copy>(s: &[T]) -> T {
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let mut total = s[0];
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for i in 1..s.len() {
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total += s[i];
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}
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total
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}
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fn find<T>(s: &[T], f: fn(&T) -> bool) -> Option<&T> { // only works for functions f
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for x in s {
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if f(x) {
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return Some(x);
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}
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}
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None
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}
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fn find2<T, F>(s: &[T], f: F) -> Option<&T> // works for both functions & closures
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where F: Fn(&T) -> bool {
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for x in s {
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if f(x) {
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return Some(x);
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}
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}
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None
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}
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fn main() {
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let v = vec![3, 2, 7, 6, 8];
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println!("{}", sum(&v));
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let v = vec![3.1, 2.0, 7.3, 6.1, 8.0];
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println!("{}", sum(&v));
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let v = vec![3, 2, 7, 6, 8];
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fn is_even(x: &i32) -> bool {
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x % 2 == 0
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}
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if let Some(r) = find(&v, is_even) {
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println!("{r}");
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}
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let divisor = 2;
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/*
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fn divisible(x: &i32) -> bool {
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x % divisor == 0 // ERROR: can't capture divisor
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}
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*/
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// let divisible = |x: &i32| -> bool { x % divisor == 0 }; // closure; can capture environment
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let divisible = |x: &i32| { x % divisor == 0 }; // closure; can capture environment
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/*
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if let Some(r) = find(&v, divisible) { // ERROR: A closure is not regular fn
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println!("{r}");
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}
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*/
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if let Some(r) = find2(&v, divisible) { // OK
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println!("{r}");
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}
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/*
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if let Some(r) = find2(&v, is_even) { // OK, also works for regular function
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println!("{r}");
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}
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*/
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}
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