编译如下：
pub fn build_proverb(list: &[&str]) -> String {
if list.is_empty() {
return String::new();
}
let mut result = (0..list.len() - 1)
.map(|i| format!("For want of a {} the {} was lost.", list[i], list[i + 1]))
.collect::<Vec<String>>();
result.push(format!("And all for the want of a {}.", list[0]));
result.join("\n")
}
以下不是（请参见Playground）：
pub fn build_proverb(list: &[&str]) -> String {
if list.is_empty() {
return String::new();
}
let mut result = (0..list.len() - 1)
.map(|i| format!("For want of a {} the {} was lost.", …