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spec: adjust type identity rules for type parameters

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Change-Id: I5ffc7f26236487070447eaa0f6b14d1fab44c3c7
Reviewed-on: https://go-review.googlesource.com/c/go/+/366794
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This commit is contained in:
Robert Griesemer 2021-11-23 18:11:07 -08:00
parent a3b8f627c2
commit 6ea17aa52c
1 changed files with 19 additions and 10 deletions
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29
doc/go_spec.html
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@ -1750,7 +1750,7 @@ Two types are either <i>identical</i> or <i>different</i>.
</p>
<p>
A <a href="#Type_definitions">defined type</a> is always different from any other type.
A <a href="#Types">named type</a> is always different from any other type.
Otherwise, two types are identical if their <a href="#Types">underlying</a> type literals are
structurally equivalent; that is, they have the same literal structure and corresponding
components have identical types. In detail:
@ -1775,15 +1775,17 @@ components have identical types. In detail:
identical, and either both functions are variadic or neither is.
Parameter and result names are not required to match.</li>
<li>Two interface types are identical if they have the same set of methods
with the same names and identical function types.
<a href="#Exported_identifiers">Non-exported</a> method names from different
packages are always different. The order of the methods is irrelevant.</li>
<li>Two interface types are identical if they define the same type set.
</li>
<li>Two map types are identical if they have identical key and element types.</li>
<li>Two channel types are identical if they have identical element types and
the same direction.</li>
<li>Two <a href="#Instantiations">instantiated</a> types are identical if
their defined types and all type arguments are identical.
</li>
</ul>
<p>
@ -1798,18 +1800,18 @@ type (
A3 = int
A4 = func(A3, float64) *A0
A5 = func(x int, _ float64) *[]string
)
type (
B0 A0
B1 []string
B2 struct{ a, b int }
B3 struct{ a, c int }
B4 func(int, float64) *B0
B5 func(x int, y float64) *A1
)
type C0 = B0
C0 = B0
D0[P1, P2 any] struct{ x P1; y P2 }
E0 = D0[int, string]
)
</pre>
<p>
@ -1823,6 +1825,7 @@ A3 and int
A4, func(int, float64) *[]string, and A5
B0 and C0
D0[int, string] and E0
[]int and []int
struct{ a, b *T5 } and struct{ a, b *T5 }
func(x int, y float64) *[]string, func(int, float64) (result *[]string), and A5
@ -1832,7 +1835,13 @@ func(x int, y float64) *[]string, func(int, float64) (result *[]string), and A5
<code>B0</code> and <code>B1</code> are different because they are new types
created by distinct <a href="#Type_definitions">type definitions</a>;
<code>func(int, float64) *B0</code> and <code>func(x int, y float64) *[]string</code>
are different because <code>B0</code> is different from <code>[]string</code>.
are different because <code>B0</code> is different from <code>[]string</code>;
and <code>P1</code> and <code>P2</code> are different because they are different
type parameters.
<code>D0[int, string]</code> and <code>struct{ x int; y string }</code> are
different because the former is an <a href="#Instantiations">instantiated</a>
defined type while the latter is a type literal
(but they are still <a href="#Assignability">assignable</a>).
</p>
<h3 id="Assignability">Assignability</h3>