From 5b03ea6ca559b9e28cc64e7805e89be013fb79aa Mon Sep 17 00:00:00 2001
From: "Dustin J. Mitchell" <djmitche@google.com>
Date: Wed, 22 Jan 2025 11:45:01 -0500
Subject: [PATCH] Add empty structs (#2569)
This should be quick, but introduces the syntax and the concept of a
ZST.
---
src/user-defined-types/tuple-structs.md | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/src/user-defined-types/tuple-structs.md b/src/user-defined-types/tuple-structs.md
index 653e8741..53dd2b8f 100644
--- a/src/user-defined-types/tuple-structs.md
+++ b/src/user-defined-types/tuple-structs.md
@@ -2,10 +2,6 @@
minutes: 10
---
-<!-- NOTES:
-Tuple structs, newtype wrappers, unit-like structs, including initialization syntax
--->
-
# Tuple Structs
If the field names are unimportant, you can use a tuple struct:
@@ -52,6 +48,12 @@ fn main() {
- Rust generally doesn’t like inexplicit things, like automatic unwrapping or
for instance using booleans as integers.
- Operator overloading is discussed on Day 3 (generics).
+- When a tuple struct has zero fields, the `()` can be omitted. The result is a
+ zero-sized type (ZST), of which there is only one value (the name of the
+ type).
+ - This is common for types that implement some behavior but have no data
+ (imagine a `NullReader` that implements some reader behavior by always
+ returning EOF).
- The example is a subtle reference to the
[Mars Climate Orbiter](https://en.wikipedia.org/wiki/Mars_Climate_Orbiter)
failure.