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spec: clarify value passed for final parameter of variadic functions

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NOT A LANGUAGE CHANGE.

Fixes #7073.

LGTM=r
R=r, rsc, iant, ken
CC=golang-codereviews
https://golang.org/cl/68840045
This commit is contained in:
Robert Griesemer 2014-03-06 10:35:05 -08:00
parent 8ca3372d7b
commit a766277742
1 changed files with 15 additions and 10 deletions
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doc/go_spec.html
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@ -2915,27 +2915,32 @@ There is no distinct method type and there are no method literals.
<h3 id="Passing_arguments_to_..._parameters">Passing arguments to <code>...</code> parameters</h3>
<p>
If <code>f</code> is variadic with final parameter type <code>...T</code>,
then within the function the argument is equivalent to a parameter of type
<code>[]T</code>. At each call of <code>f</code>, the argument
passed to the final parameter is
a new slice of type <code>[]T</code> whose successive elements are
the actual arguments, which all must be <a href="#Assignability">assignable</a>
to the type <code>T</code>. The length of the slice is therefore the number of
arguments bound to the final parameter and may differ for each call site.
If <code>f</code> is <a href="#Function_types">variadic</a> with a final
parameter <code>p</code> of type <code>...T</code>, then within <code>f</code>
the type of <code>p</code> is equivalent to type <code>[]T</code>.
If <code>f</code> is invoked with no actual arguments for <code>p</code>,
the value passed to <code>p</code> is <code>nil</code>.
Otherwise, the value passed is a new slice
of type <code>[]T</code> with a new underlying array whose successive elements
are the actual arguments, which all must be <a href="#Assignability">assignable</a>
to <code>T</code>. The length and capacity of the slice is therefore
the number of arguments bound to <code>p</code> and may differ for each
call site.
</p>
<p>
Given the function and call
Given the function and calls
</p>
<pre>
func Greeting(prefix string, who ...string)
Greeting("nobody")
Greeting("hello:", "Joe", "Anna", "Eileen")
</pre>
<p>
within <code>Greeting</code>, <code>who</code> will have the value
<code>[]string{"Joe", "Anna", "Eileen"}</code>
<code>nil</code> in the first call, and
<code>[]string{"Joe", "Anna", "Eileen"}</code> in the second.
</p>
<p>