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// issue: #110623
//@ check-pass
use std::{collections::BTreeMap, num::ParseIntError, str::FromStr};
enum FileSystem {
File(usize),
Directory(BTreeMap<String, FileSystem>),
}
impl FromStr for FileSystem {
type Err = ParseIntError;
fn from_str(s: &str) -> Result<Self, Self::Err> {
if s.starts_with("dir") {
Ok(Self::new_dir())
} else {
Ok(Self::File(s.split_whitespace().next().unwrap().parse()?))
}
}
}
impl FileSystem {
fn new_dir() -> FileSystem {
FileSystem::Directory(BTreeMap::new())
}
fn insert(&mut self, name: String, other: FileSystem) -> Option<FileSystem> {
match self {
FileSystem::File(_) => panic!("can only insert into directory!"),
FileSystem::Directory(tree) => tree.insert(name, other),
}
}
// Recursively build a tree from commands. This uses (abuses?)
// the fact that `cd /` only appears at the start and that
// subsequent `cd`s can only move ONE level to use the recursion
// stack as the filesystem stack
fn build<'a>(
&mut self,
mut commands: impl Iterator<Item = &'a str> + 'a,
) -> Option<impl Iterator<Item = &'a str> + 'a> {
let cmd = commands.next()?;
let mut elements = cmd.lines();
match elements.next().map(str::trim) {
Some("cd /") | None => self.build(commands),
Some("cd ..") => {
// return to higher scope
Some(commands)
}
Some("ls") => {
for item in elements {
let name = item.split_whitespace().last().unwrap();
let prior = self.insert(name.to_string(), item.parse().unwrap());
debug_assert!(prior.is_none());
}
// continue on
self.build(commands)
}
Some(other_cd) => {
let name = other_cd
.trim()
.strip_prefix("cd ")
.expect("expected a cd command");
let mut directory = FileSystem::new_dir();
let further_commands = directory.build(commands);
self.insert(name.to_string(), directory);
self.build(further_commands?) // THIS LINE FAILS TO COMPILE
}
}
}
}
fn main() {}
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