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Allow optional second expression in slice expressions.

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Built-in function copy.
Addresses issue 203.

R=rsc, r, iant
https://golang.org/cl/156089
This commit is contained in:
Robert Griesemer 2009-11-18 19:15:25 -08:00
parent e1c5c3df77
commit 1a8ebcc4b8
1 changed files with 51 additions and 12 deletions
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63
doc/go_spec.html
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@ -2097,7 +2097,7 @@ PrimaryExpr =
Selector = "." identifier .
Index = "[" Expression "]" .
Slice = "[" Expression ":" Expression "]" .
Slice = "[" Expression ":" [ Expression ] "]" .
TypeAssertion = "." "(" Type ")" .
Call = "(" [ ExpressionList ] ")" .
</pre>
@ -2330,28 +2330,39 @@ a regular assignment to an element of the map.
<h3 id="Slices">Slices</h3>
<p>
Strings, arrays, and slices can be <i>sliced</i> to construct substrings or descriptors
of subarrays. The index expressions in the slice select which elements appear
in the result. The result has indexes starting at 0 and length equal to the
difference in the index values in the slice. After slicing the array <code>a</code>
For a string, array, or slice <code>a</code>, the primary expression
</p>
<pre>
a := [4]int{1, 2, 3, 4};
s := a[1:3];
a[lo : hi]
</pre>
<p>
the slice <code>s</code> has type <code>[]int</code>, length 2, capacity 3, and elements
constructs a substring or slice. The index expressions <code>lo</code> and
<code>hi</code> select which elements appear in the result. The result has
indexes starting at 0 and length equal to
<code>hi</code>&nbsp;-&nbsp;<code>lo</code>.
After slicing the array <code>a</code>
</p>
<pre>
a := [5]int{1, 2, 3, 4, 5};
s := a[1:4];
</pre>
<p>
the slice <code>s</code> has type <code>[]int</code>, length 3, capacity 4, and elements
</p>
<pre>
s[0] == 2
s[1] == 3
s[2] == 4
</pre>
<p>
The slice length must not be negative.
For convenience, the <code>hi</code> expression may be omitted; the notation
<code>a[lo :]</code> is shorthand for <code>a[lo : len(a)]</code>.
For arrays or strings, the indexes
<code>lo</code> and <code>hi</code> must satisfy
0 &lt;= <code>lo</code> &lt;= <code>hi</code> &lt;= length;
@ -2461,7 +2472,7 @@ assignment of regular parameters.
<pre>
func Split(s string, pos int) (string, string) {
return s[0:pos], s[pos:len(s)]
return s[0:pos], s[pos:]
}
func Join(s, t string) string {
@ -4137,7 +4148,7 @@ The memory is initialized as described in the section on initial values
(§<a href="#The_zero_value">The zero value</a>).
</p>
<pre>
<pre class="grammar">
new(T)
</pre>
@ -4170,7 +4181,7 @@ The memory is initialized as described in the section on initial values
(§<a href="#The_zero_value">The zero value</a>).
</p>
<pre>
<pre class="grammar">
make(T [, optional list of expressions])
</pre>
@ -4199,6 +4210,34 @@ m := make(map[string] int, 100); // map with initial space for 100 elements
</pre>
<h3 id="Copying_slices">Copying slices</h3>
<p>
The built-in function <code>copy</code> copies array or slice elements from
a source <code>src</code> to a destination <code>dst</code> and returns the
number of elements copied. Source and destination may overlap.
Both arguments must have the same element type <code>T</code> and must be
<a href="#Assignment_compatibility">assignment compatible</a> to a slice
of type <code>[]T</code>. The number of arguments copied is the minimum of
<code>len(src)</code> and <code>len(dst)</code>.
</p>
<pre class="grammar">
copy(dst, src []T) int
</pre>
<p>
Examples:
</p>
<pre>
var a = [...]int{0, 1, 2, 3, 4, 5, 6, 7};
var s = make([]int, 6);
n1 := copy(s, &amp;a); // n1 == 6, s == []int{0, 1, 2, 3, 4, 5}
n2 := copy(s, s[2:]); // n2 == 4, s == []int{2, 3, 4, 5, 4, 5}
</pre>
<h3 id="Bootstrapping">Bootstrapping</h3>
<p>