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add definition of new parameter style

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... T
for trailing arguments of type T.

R=rsc, gri, ken2, iant
CC=golang-dev
https://golang.org/cl/194100
This commit is contained in:
Rob Pike 2010-01-27 13:14:40 -08:00
parent e0afb0c38b
commit b81065d07f
1 changed files with 51 additions and 17 deletions
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68
doc/go_spec.html
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@ -900,7 +900,7 @@ Signature = Parameters [ Result ] .
Result = Parameters | Type .
Parameters = "(" [ ParameterList [ "," ] ] ")" .
ParameterList = ParameterDecl { "," ParameterDecl } .
ParameterDecl = [ IdentifierList ] ( Type | "..." ) .
ParameterDecl = [ IdentifierList ] ( Type | "..." [ Type ] ) .
</pre>
<p>
@ -913,9 +913,12 @@ one unnamed result it may written as an unparenthesized type.
</p>
<p>
For the last parameter only, instead of a type one may write
<code>...</code> to indicate that the function may be invoked with
zero or more additional arguments of any
type.
<code>...</code> or <code>... T</code> to indicate that the function
may be invoked with zero or more additional arguments. If the type
<code>T</code> is present in the parameter declaration, the additional
arguments must all be
<a href="#Assignment_compatibility">assignment compatible</a>
with type <code>T</code>; otherwise they may be of any type.
</p>
<pre>
@ -923,6 +926,7 @@ func()
func(x int)
func() int
func(string, float, ...)
func(prefix string, values ... int)
func(a, b int, z float) bool
func(a, b int, z float) (bool)
func(a, b int, z float, opt ...) (success bool)
@ -1189,7 +1193,9 @@ identical types. In detail:
<li>Two function types are identical if they have the same number of parameters
and result values and if corresponding parameter and result types are
identical. All "..." parameters are defined to have identical type.
identical. All "..." parameters without a specified type are defined to have
identical type. All "..." parameters with specified identical type
<code>T</code> are defined to have identical type.
Parameter and result names are not required to match.</li>
<li>Two interface types are identical if they have the same set of methods
@ -2596,15 +2602,15 @@ parameter.
</p>
<p>
Within <code>f</code>, the <code>...</code> parameter has static
type <code>interface{}</code> (the empty interface). For each call,
its dynamic type is a structure whose sequential fields are the
trailing arguments of the call. That is, the actual arguments
provided for a <code>...</code> parameter are wrapped into a struct
that is passed to the function instead of the actual arguments.
Using the <a href="#Package_unsafe">reflection</a> interface, <code>f</code> may
unpack the elements of the dynamic type to recover the actual
arguments.
Within <code>f</code>, a <code>...</code> parameter with no
specified type has static type <code>interface{}</code> (the empty
interface). For each call, its dynamic type is a structure whose
sequential fields are the trailing arguments of the call. That is,
the actual arguments provided for a <code>...</code> parameter are
wrapped into a struct that is passed to the function instead of the
actual arguments. Using the <a href="#Package_unsafe">reflection</a>
interface, <code>f</code> may unpack the elements of the dynamic
type to recover the actual arguments.
</p>
<p>
@ -2621,12 +2627,40 @@ call will be, schematically,
<code> struct { string; int }</code>.
</p>
<p>
If the final parameter of <code>f</code> has type <code>... T</code>,
within the function it is equivalent to a parameter of type
<code>[]T</code>. At each call of <code>f</code>, the actual
arguments provided for the <code>... T</code> parameter are placed
into a new slice of type <code>[]T</code> whose successive elements are
the actual arguments. The length of the slice is therefore the
number of arguments bound to the <code>... T</code> parameter and
may differ for each call site.
</p>
<p>
As a special case, if a function passes its own <code>...</code> parameter as the argument
for a <code>...</code> in a call to another function with a <code>...</code> parameter,
Given the function and call
</p>
<pre>
func Greeting(prefix string, who ... string)
Greeting("hello:", "Joe", "Anna", "Eileen")
</pre>
<p>
Within <code>Greeting</code>, <code>who</code> will have value
<code>[]string{"Joe", "Anna", "Eileen")</code>
</p>
<p>
As a special case, if a function passes its own <code>...</code> parameter,
with or without specified type, as the argument
for a <code>...</code> in a call to another function with a <code>...</code> parameter
of identical type,
the parameter is not wrapped again but passed directly. In short, a formal <code>...</code>
parameter is passed unchanged as an actual <code>...</code> parameter.
parameter is passed unchanged as an actual <code>...</code> parameter provided the
types match.
</p>
<h3 id="Operators">Operators</h3>