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spec: highlight missing prose for easier review, fixed a few sections

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The (temporary) highlights will make it easier to review the spec
in formatted form as opposed to html text.

Added a missing rule about the use of adjusted core types for
constraint type inference.

Adjusted rule for invalid embedding of interface types.

Change-Id: Ie573068d2307b66c937e803c486724175415b9c6
Reviewed-on: https://go-review.googlesource.com/c/go/+/385535
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This commit is contained in:
Robert Griesemer 2022-02-11 12:18:33 -08:00
parent 93b5309f0a
commit badbc52d82
1 changed files with 36 additions and 21 deletions
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57
doc/go_spec.html
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@ -1,6 +1,6 @@
<!--{
"Title": "The Go Programming Language Specification - Go 1.18 Draft",
"Subtitle": "Version of Feb 11, 2022",
"Subtitle": "Version of Feb 14, 2022",
"Path": "/ref/spec"
}-->
@ -11,6 +11,11 @@ For the pre-Go1.18 specification without generics support see
<a href="/doc/go1.17_spec.html">The Go Programming Language Specification</a>.
</p>
<!-- TODO(gri) remove this before the final release -->
<p><b>
[For reviewers: Sections where we know of missing prose are marked like this. The markers will be removed before the release.]
</b></p>
<h2 id="Introduction">Introduction</h2>
<p>
@ -1498,15 +1503,9 @@ type Floatish struct {
}
</pre>
<!-- TODO The rule below needs to be generalized to interface elements.
It should be factored out and generalized to other types
such as arrays and structs which are currently missing such a
rule. See also #5069.
-->
<p>
An interface type <code>T</code> may not embed itself
or any interface type that embeds <code>T</code>, recursively.
An interface type <code>T</code> may not embed any type element
that is, contains, or embeds <code>T</code>, recursively.
</p>
<pre>
@ -1522,6 +1521,11 @@ type Bad1 interface {
type Bad2 interface {
Bad1
}
// illegal: Bad3 cannot embed a union containing Bad3
type Bad3 interface {
~int | ~string | Bad3
}
</pre>
<h4 id="Implementing_an_interface">Implementing an interface</h4>
@ -1803,6 +1807,10 @@ interface{ &lt;-chan int | chan&lt;- int } // directional channels have dif
<h3 id="Specific_types">Specific types</h3>
<p><b>
[The definition of specific types is not quite correct yet.]
</b></p>
<p>
An interface specification that contains <a href="#Interface_types">type elements</a>
defines a (possibly empty) set of <i>specific types</i>.
@ -3346,7 +3354,9 @@ f.p[i].x()
<h3 id="Selectors">Selectors</h3>
<!-- This is missing rules for x of type parameter type. -->
<p><b>
[This section is missing rules for x.f where x's type is a type parameter and f is a field.]
</b></p>
<p>
For a <a href="#Primary_expressions">primary expression</a> <code>x</code>
@ -4557,14 +4567,6 @@ ensures that type inference does not depend on the order of the untyped argument
<h4 id="Constraint_type_inference">Constraint type inference</h4>
<!--
The next paragraph needs to be updated for the new definition of core type:
The core type of an interface is the single underlying type of its type set,
if it exists. But for constraint type inference, if the type set consists of exactly
one type, we want to use that one type (which may be a defined type, different from
its underlying == core type).
-->
<p>
Constraint type inference infers type arguments by considering type constraints.
If a type parameter <code>P</code> has a constraint with a
@ -4604,6 +4606,17 @@ Thus, in this example, constraint type inference can infer the second type argum
first one.
</p>
<p>
Using the core type of a constraint may lose some information: In the (unlikely) case that
the constraint's type set contains a single <a href="#Type_definitions">defined type</a>
<code>N</code>, the corresponding core type is <code>N</code>'s underlying type rather than
<code>N</code> itself. In this case, constraint type inference may succeed but instantiation
will fail because the inferred type is not in the type set of the constraint.
Thus, constraint type inference uses the <i>adjusted core type</i> of
a constraint: if the type set contains a single type, use that type; otherwise use the
constraint's core type.
</p>
<p>
Generally, constraint type inference proceeds in two phases: Starting with a given
substitution map <i>M</i>
@ -4611,7 +4624,7 @@ substitution map <i>M</i>
<ol>
<li>
For all type parameters with a core type, unify the type parameter with the core
For all type parameters with an adjusted core type, unify the type parameter with that
type. If any unification fails, constraint type inference fails.
</li>
@ -5369,7 +5382,7 @@ in any of these cases:
</ul>
<p>
Additionally, if <code>T</code> or </code><code>x's</code> type <code>V</code> are type
Additionally, if <code>T</code> or <code>x</code>'s type <code>V</code> are type
parameters with <a href="#Specific_types">specific types</a>, <code>x</code>
can also be converted to type <code>T</code> if one of the following conditions applies:
</p>
@ -7317,7 +7330,9 @@ does not exist, <code>delete</code> is a no-op.
<h3 id="Complex_numbers">Manipulating complex numbers</h3>
<!-- We don't support generic arguments for these operations yet. -->
<p><b>
[We don't support generic arguments for these built-ins for Go 1.18.]
</b></p>
<p>
Three functions assemble and disassemble complex numbers.