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doc: add FAQ: why no conversion from []T1 to []T2?

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Fixes #16934.

Change-Id: I725704e4c4aae7023fd89edc42af7ba0d242fec8
Reviewed-on: https://go-review.googlesource.com/33327
Reviewed-by: Rob Pike <r@golang.org>
This commit is contained in:
Ian Lance Taylor 2016-11-16 11:23:53 -08:00
parent 48858a2386
commit fbf92436b9
1 changed files with 23 additions and 0 deletions
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doc/go_faq.html
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@ -769,6 +769,29 @@ for i, v := range t {
}
</pre>
<h3 id="convert_slice_with_same_underlying_type">
Can I convert []T1 to []T2 if T1 and T2 have the same underlying type?</h3>
This last line of this code sample does not compile.
<pre>
type T1 int
type T2 int
var t1 T1
var x = T2(t1) // OK
var st1 []T1
var sx = ([]T2)(st1) // NOT OK
</pre>
<p>
In Go, types are closely tied to methods, in that every named type has
a (possibly empty) method set.
The general rule is that you can change the name of the type being
converted (and thus possibly change its method set) but you can't
change the name (and method set) of elements of a composite type.
Go requires you to be explicit about type conversions.
</p>
<h3 id="nil_error">
Why is my nil error value not equal to nil?
</h3>