From 450429a52932511243399dd51d370c0872d5f0a1 Mon Sep 17 00:00:00 2001
From: Nugine <nugine@foxmail.com>
Date: Sun, 26 Jan 2025 19:47:15 +0800
Subject: [PATCH] feat: add chain!

---
 const-str/src/__ctfe/chain.rs | 53 +++++++++++++++++++++++++++++++++++
 const-str/src/lib.rs          |  3 ++
 2 files changed, 56 insertions(+)
 create mode 100644 const-str/src/__ctfe/chain.rs

diff --git a/const-str/src/__ctfe/chain.rs b/const-str/src/__ctfe/chain.rs
new file mode 100644
index 0000000..0b2b20c
--- /dev/null
+++ b/const-str/src/__ctfe/chain.rs
@@ -0,0 +1,53 @@
+/// Chains multiple macro calls together.
+///
+/// `_` is used as a placeholder for the value that is being passed through the chained calls.
+///
+/// # Examples
+///
+/// ```
+/// use const_str::{chain, concat, replace, split};
+///
+/// const TOP: &str = "std";
+///
+/// const PARTS: &[&str] = &chain! {
+///    stringify!(std::sync::atomic::Ordering::Relaxed),
+///    replace!(_, { concat!(TOP, "::") }, ""),
+///    split!(_, "::"),
+/// };
+///
+/// assert_eq!(PARTS, &["sync", "atomic", "Ordering", "Relaxed"]);
+/// ```
+#[macro_export]
+macro_rules! chain {
+    ($init:expr, $( $call:ident!($($arg:tt),+), )+) => {
+        $crate::__chain_impl!(@chain $init, $( $call!($($arg),+) ),+)
+    };
+}
+
+#[doc(hidden)]
+#[macro_export]
+macro_rules! __chain_impl {
+    (@chain $init:expr, $call:ident!($($arg:tt),+)) => {
+        $crate::__chain_impl!(@call $init, $call!($($arg),+))
+    };
+
+    (@chain $init:expr, $call:ident!($($arg:tt),+), $($rest:tt)+) => {
+        $crate::__chain_impl!(@chain $crate::__chain_impl!(@call $init, $call!($($arg),+)), $($rest)+)
+    };
+
+    (@call $e: expr, $call:ident!($($arg:tt),+)) => {
+        $call!(
+            $(
+                $crate::__chain_impl!(@replace $e, $arg)
+            ),+
+        )
+    };
+
+    (@replace $e:expr, _) => {
+        $e
+    };
+
+    (@replace $e:expr, $tt:tt) => {
+        $tt
+    };
+}
diff --git a/const-str/src/lib.rs b/const-str/src/lib.rs
index 0b61f8c..955c038 100644
--- a/const-str/src/lib.rs
+++ b/const-str/src/lib.rs
@@ -66,6 +66,9 @@ pub mod __ctfe {
     mod ascii_case;
     pub use self::ascii_case::*;
 
+    mod chain;
+    // pub use self::chain::*;
+
     mod compare;
     pub use self::compare::*;