Add input! implementation for the examples

Author: qryxip

Cargo.toml

@@ -15,5 +15,6 @@ publish = false
 [dependencies]
 
 [dev-dependencies]
+input = { path = "./crates/input" }
 proconio = "=0.3.6"
 rand = "0.7.3"

crates/input/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "input"
+version = "0.1.0"
+authors = ["rust-lang-ja Developers"]
+edition = "2018"
+description = "Provides a `input!` macro for the `examples`."
+license = "CC0-1.0"
+publish = false
+
+[dependencies]

crates/input/src/lib.rs

@@ -0,0 +1,96 @@
+//! A simple `input!` macro with minimal functionality.
+//!
+//! ```no_run
+//! #[macro_use]
+//! extern crate input as _;
+//!
+//! fn main() {
+//!     input! {
+//!         a: [u64],
+//!     }
+//! }
+//! ```
+
+use std::{
+    fmt,
+    io::{self, Read},
+    str::{FromStr, SplitAsciiWhitespace},
+};
+
+#[macro_export]
+macro_rules! input {
+    ($($tt:tt)*) => {
+        let mut __scanner = $crate::Scanner::new().unwrap();
+        $crate::input_inner!(@scanner(__scanner), @tts($($tt)*));
+        ::std::mem::drop(__scanner);
+    };
+}
+
+#[doc(hidden)]
+#[macro_export]
+macro_rules! input_inner {
+    (@scanner($scanner:ident), @tts()) => {};
+    (@scanner($scanner:ident), @tts(mut $single_tt_pat:tt : $readable:tt)) => {
+        let mut $single_tt_pat = $crate::read!(from $scanner { $readable });
+    };
+    (@scanner($scanner:ident), @tts($single_tt_pat:tt : $readable:tt)) => {
+        let $single_tt_pat = $crate::read!(from $scanner { $readable });
+    };
+    (@scanner($scanner:ident), @tts(mut $single_tt_pat:tt : $readable:tt, $($rest:tt)*)) => {
+        $crate::input_inner!(@scanner($scanner), @tts(mut $single_tt_pat: $readable));
+        $crate::input_inner!(@scanner($scanner), @tts($($rest)*));
+    };
+    (@scanner($scanner:ident), @tts($single_tt_pat:tt : $readable:tt, $($rest:tt)*)) => {
+        $crate::input_inner!(@scanner($scanner), @tts($single_tt_pat: $readable));
+        $crate::input_inner!(@scanner($scanner), @tts($($rest)*));
+    };
+}
+
+#[doc(hidden)]
+#[macro_export]
+macro_rules! read {
+    (from $scanner:ident { [$tt:tt] }) => {
+        $crate::read!(from $scanner { [$tt; $crate::read!(from $scanner { usize })] })
+    };
+    (from $scanner:ident  { [$tt:tt; $n:expr] }) => {
+        (0..$n).map(|_| $crate::read!(from $scanner { $tt })).collect::<Vec<_>>()
+    };
+    (from $scanner:ident { ($($tt:tt),+) }) => {
+        ($($crate::read!(from $scanner { $tt })),*)
+    };
+    (from $scanner:ident { $ty:ty }) => {
+        $scanner.parse::<$ty>()
+    };
+}
+
+#[doc(hidden)]
+pub struct Scanner {
+    words: SplitAsciiWhitespace<'static>,
+}
+
+impl Scanner {
+    pub fn new() -> io::Result<Self> {
+        let mut buf = String::with_capacity(1024);
+        io::stdin().read_to_string(&mut buf)?;
+        let words = Box::leak(buf.into_boxed_str()).split_ascii_whitespace();
+        Ok(Self { words })
+    }
+
+    /// Parses the next word.
+    ///
+    /// # Panics
+    ///
+    /// Panics if:
+    ///
+    /// - reached the end of input.
+    /// - the word is not successfully parsed.
+    pub fn parse<T>(&mut self) -> T
+    where
+        T: FromStr,
+        T::Err: fmt::Display,
+    {
+        let word = self.words.next().expect("reached the end of input");
+        word.parse()
+            .unwrap_or_else(|e| panic!("could not parse {:?}: {}", word, e))
+    }
+}