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use std::collections::HashSet;
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use std::io::{stderr, Write};
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fn main() {
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let nothing = HashSet::new();
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let mut things = HashSet::new();
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things.insert(42);
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unwrap_print_set_element(things);
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unwrap_print_set_element(nothing);
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}
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fn unwrap_print_set_element(elements: HashSet<i32>) {
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let mut iterator = elements.iter();
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if let Some(element) = iterator.next() {
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writeln!(stderr(), "set element: {}", element).ok();
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}
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}
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