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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>
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@ -1,6 +1,6 @@
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<!--{
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"Title": "The Go Programming Language Specification",
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"Subtitle": "Version of September 1, 2016",
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"Subtitle": "Version of October 4, 2016",
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"Path": "/ref/spec"
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}-->
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@ -3837,10 +3837,12 @@ in any of these cases:
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to <code>T</code>.
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</li>
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<li>
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<code>x</code>'s type and <code>T</code> have identical
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ignoring struct tags (see below),
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<code>x</code>'s type and <code>T</code> have <a href="#Type_identity">identical</a>
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<a href="#Types">underlying types</a>.
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</li>
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<li>
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ignoring struct tags (see below),
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<code>x</code>'s type and <code>T</code> are unnamed pointer types
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and their pointer base types have identical underlying types.
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</li>
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@ -3860,6 +3862,31 @@ in any of these cases:
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</li>
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</ul>
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<p>
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<a href="#Struct_types">Struct tags</a> are ignored when comparing struct types
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for identity for the purpose of conversion:
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</p>
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<pre>
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type Person struct {
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Name string
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Address *struct {
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Street string
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City string
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}
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}
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var data *struct {
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Name string `json:"name"`
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Address *struct {
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Street string `json:"street"`
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City string `json:"city"`
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} `json:"address"`
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}
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var person = (*Person)(data) // ignoring tags, the underlying types are identical
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</pre>
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<p>
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Specific rules apply to (non-constant) conversions between numeric types or
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to and from a string type.
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