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Allow optional second expression in slice expressions.
Built-in function copy. Addresses issue 203. R=rsc, r, iant https://golang.org/cl/156089
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@ -2097,7 +2097,7 @@ PrimaryExpr =
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Selector = "." identifier .
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Index = "[" Expression "]" .
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Slice = "[" Expression ":" Expression "]" .
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Slice = "[" Expression ":" [ Expression ] "]" .
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TypeAssertion = "." "(" Type ")" .
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Call = "(" [ ExpressionList ] ")" .
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</pre>
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@ -2330,28 +2330,39 @@ a regular assignment to an element of the map.
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<h3 id="Slices">Slices</h3>
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<p>
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Strings, arrays, and slices can be <i>sliced</i> to construct substrings or descriptors
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of subarrays. The index expressions in the slice select which elements appear
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in the result. The result has indexes starting at 0 and length equal to the
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difference in the index values in the slice. After slicing the array <code>a</code>
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For a string, array, or slice <code>a</code>, the primary expression
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</p>
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<pre>
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a := [4]int{1, 2, 3, 4};
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s := a[1:3];
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a[lo : hi]
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</pre>
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<p>
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the slice <code>s</code> has type <code>[]int</code>, length 2, capacity 3, and elements
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constructs a substring or slice. The index expressions <code>lo</code> and
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<code>hi</code> select which elements appear in the result. The result has
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indexes starting at 0 and length equal to
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<code>hi</code> - <code>lo</code>.
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After slicing the array <code>a</code>
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</p>
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<pre>
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a := [5]int{1, 2, 3, 4, 5};
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s := a[1:4];
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</pre>
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<p>
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the slice <code>s</code> has type <code>[]int</code>, length 3, capacity 4, and elements
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</p>
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<pre>
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s[0] == 2
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s[1] == 3
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s[2] == 4
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</pre>
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<p>
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The slice length must not be negative.
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For convenience, the <code>hi</code> expression may be omitted; the notation
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<code>a[lo :]</code> is shorthand for <code>a[lo : len(a)]</code>.
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For arrays or strings, the indexes
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<code>lo</code> and <code>hi</code> must satisfy
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0 <= <code>lo</code> <= <code>hi</code> <= length;
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@ -2461,7 +2472,7 @@ assignment of regular parameters.
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<pre>
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func Split(s string, pos int) (string, string) {
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return s[0:pos], s[pos:len(s)]
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return s[0:pos], s[pos:]
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}
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func Join(s, t string) string {
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@ -4137,7 +4148,7 @@ The memory is initialized as described in the section on initial values
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(§<a href="#The_zero_value">The zero value</a>).
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</p>
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<pre>
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<pre class="grammar">
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new(T)
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</pre>
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@ -4170,7 +4181,7 @@ The memory is initialized as described in the section on initial values
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(§<a href="#The_zero_value">The zero value</a>).
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</p>
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<pre>
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<pre class="grammar">
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make(T [, optional list of expressions])
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</pre>
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@ -4199,6 +4210,34 @@ m := make(map[string] int, 100); // map with initial space for 100 elements
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</pre>
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<h3 id="Copying_slices">Copying slices</h3>
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<p>
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The built-in function <code>copy</code> copies array or slice elements from
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a source <code>src</code> to a destination <code>dst</code> and returns the
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number of elements copied. Source and destination may overlap.
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Both arguments must have the same element type <code>T</code> and must be
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<a href="#Assignment_compatibility">assignment compatible</a> to a slice
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of type <code>[]T</code>. The number of arguments copied is the minimum of
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<code>len(src)</code> and <code>len(dst)</code>.
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</p>
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<pre class="grammar">
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copy(dst, src []T) int
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</pre>
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<p>
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Examples:
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</p>
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<pre>
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var a = [...]int{0, 1, 2, 3, 4, 5, 6, 7};
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var s = make([]int, 6);
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n1 := copy(s, &a); // n1 == 6, s == []int{0, 1, 2, 3, 4, 5}
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n2 := copy(s, s[2:]); // n2 == 4, s == []int{2, 3, 4, 5, 4, 5}
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</pre>
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<h3 id="Bootstrapping">Bootstrapping</h3>
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<p>
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