languages/go
languages/go
1
0
Fork 0
mirror of https://github.com/golang/go synced 2024-09-05 16:04:50 +00:00
Code Issues Packages Projects Releases Wiki Activity

spec: describe constraint parsing ambiguity and work-around more precisely

Browse source 
The new description matches the implementation (CL 370774).

Also, in the section on type constraints, use "defines" instead of
"determines" because the constraint interface defines the type set
which is precisely the set of acceptable type arguments.

For #49482.

Change-Id: I6f30f49100e8ba8bec0a0f1b450f88cae54312eb
Reviewed-on: https://go-review.googlesource.com/c/go/+/372874
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This commit is contained in:
Robert Griesemer 2021-12-16 10:25:07 -08:00
parent 2bdf34f3e8
commit 3c495839fe
1 changed files with 6 additions and 3 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

9
doc/go_spec.html
View file

@ -2604,7 +2604,8 @@ has a corresponding (meta-)type which is called its
<p>
A parsing ambiguity arises when the type parameter list for a parameterized type
declares a single type parameter with a type constraint of the form <code>*C</code>
or <code>(C)</code>:
or <code>(C)</code> where <code>C</code> is not a (possibly parenthesized)
<a href="#Types">type literal</a>:
</p>
<pre>
@ -2616,17 +2617,19 @@ type T[P (C)] …
In these rare cases, the type parameter declaration is indistinguishable from
the expressions <code>P*C</code> or <code>P(C)</code> and the type declaration
is parsed as an array type declaration.
To resolve the ambiguity, embed the constraint in an interface:
To resolve the ambiguity, embed the constraint in an interface or use a trailing
comma:
</p>
<pre>
type T[P interface{*C}] …
type T[P *C,] …
</pre>
<h4 id="Type_constraints">Type constraints</h4>
<p>
A type constraint is an <a href="#Interface_types">interface</a> that determines the
A type constraint is an <a href="#Interface_types">interface</a> that defines the
set of permissible type arguments for the respective type parameter and controls the
operations supported by values of that type parameter.
</p>