spec: ignore struct tags when converting structs
This is a backwards-compatible language change.
Per the proposal (#16085), the rules for conversions are relaxed
such that struct tags in any of the structs involved in the conversion
are ignored (recursively).
Because this is loosening the existing rules, code that compiled so
far will continue to compile.
For #16085.
Fixes #6858.
Change-Id: I0feef651582db5f23046a2331fc3f179ae577c45
Reviewed-on: https://go-review.googlesource.com/24190
Reviewed-by: Russ Cox <rsc@golang.org>
diff --git a/doc/go_spec.html b/doc/go_spec.html
index 1d0ea22..6e07c94 100644
--- a/doc/go_spec.html
+++ b/doc/go_spec.html
@@ -1,6 +1,6 @@
<!--{
"Title": "The Go Programming Language Specification",
- "Subtitle": "Version of September 1, 2016",
+ "Subtitle": "Version of October 4, 2016",
"Path": "/ref/spec"
}-->
@@ -3837,10 +3837,12 @@
to <code>T</code>.
</li>
<li>
- <code>x</code>'s type and <code>T</code> have identical
+ ignoring struct tags (see below),
+ <code>x</code>'s type and <code>T</code> have <a href="#Type_identity">identical</a>
<a href="#Types">underlying types</a>.
</li>
<li>
+ ignoring struct tags (see below),
<code>x</code>'s type and <code>T</code> are unnamed pointer types
and their pointer base types have identical underlying types.
</li>
@@ -3861,6 +3863,31 @@
</ul>
<p>
+<a href="#Struct_types">Struct tags</a> are ignored when comparing struct types
+for identity for the purpose of conversion:
+</p>
+
+<pre>
+type Person struct {
+ Name string
+ Address *struct {
+ Street string
+ City string
+ }
+}
+
+var data *struct {
+ Name string `json:"name"`
+ Address *struct {
+ Street string `json:"street"`
+ City string `json:"city"`
+ } `json:"address"`
+}
+
+var person = (*Person)(data) // ignoring tags, the underlying types are identical
+</pre>
+
+<p>
Specific rules apply to (non-constant) conversions between numeric types or
to and from a string type.
These conversions may change the representation of <code>x</code>
