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spec: describe processing of function arguments for type inference more precisely

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The outcome of type inference depends critically on when function
argument type inference stops processing arguments. Describe this
and explain an example with some detail.

Also: In the section on the built-in function delete, refer to the
value rather than the type of the second argument, as it may be an
untyped constant.

Change-Id: Ice7fbb33f985afe082380b8d37eaf763238a3818
Reviewed-on: https://go-review.googlesource.com/c/go/+/385034
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This commit is contained in:
Robert Griesemer 2022-02-10 20:10:33 -08:00
parent 9fdcfb7c10
commit e50f0f372b
1 changed files with 14 additions and 1 deletions
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15
doc/go_spec.html
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@ -4514,6 +4514,12 @@ Each list is processed in a separate phase:
</li>
</ol>
<p>
While unification is successful, processing of each list continues until all list elements
are considered, even if all type arguments are inferred before the last list element has
been processed.
</p>
<p>
Example:
</p>
@ -4527,6 +4533,13 @@ min(1.0, 2.0) // T is float64, inferred from default type for 1.0 and matches d
min(1.0, 2) // illegal: default type float64 (for 1.0) doesn't match default type int (for 2)
</pre>
<p>
In the example <code>min(1.0, 2)</code>, processing the function argument <code>1.0</code>
yields the substitution map entry <code>T</code> &RightArrow; <code>float64</code>. Because
processing continues until all untyped arguments are considered, an error is reported. This
ensures that type inference does not depend on the order of the untyped arguments.
</p>
<h4 id="Constraint_type_inference">Constraint type inference</h3>
<!--
@ -7268,7 +7281,7 @@ n3 := copy(b, "Hello, World!") // n3 == 5, b == []byte("Hello")
<p>
The built-in function <code>delete</code> removes the element with key
<code>k</code> from a <a href="#Map_types">map</a> <code>m</code>. The
type of <code>k</code> must be <a href="#Assignability">assignable</a>
value <code>k</code> must be <a href="#Assignability">assignable</a>
to the key type of <code>m</code>.
</p>