From 0c53fd590e8a5885ce9ee4045c06119e48660b25 Mon Sep 17 00:00:00 2001
From: Paul Duncan <pabs@pablotron.org>
Date: Wed, 19 Jan 2022 18:00:21 -0500
Subject: content/posts/2022-01-17-generics-in-go-1.18.md: wording fixes, add
 info about tilde prefixes

---
 content/posts/2022-01-17-generics-in-go-1.18.md | 27 +++++++++++++++++--------
 1 file changed, 19 insertions(+), 8 deletions(-)

(limited to 'content/posts')

diff --git a/content/posts/2022-01-17-generics-in-go-1.18.md b/content/posts/2022-01-17-generics-in-go-1.18.md
index 5379ab7..1a44b03 100644
--- a/content/posts/2022-01-17-generics-in-go-1.18.md
+++ b/content/posts/2022-01-17-generics-in-go-1.18.md
@@ -81,7 +81,7 @@ package main
 import "fmt"
 
 // Return sum of all numeric values in slice.
-func Sum[V int|float32|complex64](vals []V) V {
+func Sum[V ~int|~float32|~complex64](vals []V) V {
   var r V
 
   for _, v := range(vals) {
@@ -133,7 +133,7 @@ package main
 import "fmt"
 
 // Fraction
-type Frac[T int|int32|int64] struct {
+type Frac[T ~int|~int32|~int64] struct {
   num T // numerator
   den T // denominator
 }
@@ -174,14 +174,22 @@ func main() {
 ```
 &nbsp;
 
-Interface type declarations can now be used to specify type unions.  For
-example, the `Frac` type declaration from the previous example could be
-written like this instead:
+Interface type declarations can now be used to define the constraints
+that a matching type must satisfy.  In addition to the ability to
+specify methods that a matching type must implement, a type constraint
+specified as an interface may also specify a union of terms indicating
+the set of matching types.
+
+Type union terms can be tilde-prefixed (example: `~int`), which
+indicates that the *underlying type* must match the given type.
+
+For example, the `Frac` type declaration from the previous example could
+be written like this instead:
 
 ```go
 // Integral number type.
 type integral interface {
-  int | int32 | int64
+  ~int | ~int32 | ~int64
 }
 
 // Fraction
@@ -192,9 +200,9 @@ type Frac[T integral] struct {
 ```
 &nbsp;
 
-There are two new keywords:
+There are two new predeclared identifiers:
 
-* `any`: Alias for `interface {}`.
+* `any`: An alias for `interface {}`.
 * `comparable`: Any type which can be compared for equality with `==`
   and `!=`.  Useful for the parameterizing map keys.
 
@@ -298,6 +306,9 @@ Other useful tidbits:
   need to rewrite your existing code.
 * There are [two new tutorials][] which explain generics and fuzzing.
 
+**Update (2021-01-19):** Minor wording changes, add information about
+tilde prefixes in type constraints.
+
 [go]: https://go.dev/
   "Go programming language"
 [go 1.18]: https://tip.golang.org/doc/go1.18
-- 
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