From 8fa48573e15b50971c8f20bea1250407ea3f586c Mon Sep 17 00:00:00 2001
From: Steve Klabnik <steve@steveklabnik.com>
Date: Tue, 9 Feb 2016 13:33:02 -0500
Subject: [PATCH] make note of arity and 32-length restriction

---
 src/libstd/primitive_docs.rs | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/libstd/primitive_docs.rs b/src/libstd/primitive_docs.rs
index 2be8c41a496e..ad93fe0094ae 100644
--- a/src/libstd/primitive_docs.rs
+++ b/src/libstd/primitive_docs.rs
@@ -366,6 +366,9 @@ mod prim_str { }
 /// ("hello", 5, 'c');
 /// ```
 ///
+/// 'Length' is also sometimes called 'arity' here; each tuple of a different
+/// length is a different, distinct type.
+///
 /// Tuples are *heterogeneous*. This means that each element of the tuple can
 /// have a different type. In that tuple above, it has the type:
 ///
@@ -409,6 +412,9 @@ mod prim_str { }
 /// [`Default`]: ../default/trait.Default.html
 /// [`Hash`]: ../hash/trait.Hash.html
 ///
+/// Due to a temporary restriction in Rust's type system, these traits are only
+/// implemented on tuples of arity 32 or less. In the future, this may change.
+///
 /// # Examples
 ///
 /// Basic usage: