spec: index and array/slice size constants must fit into an int

R=r, rsc, iant, ken
CC=golang-dev
https://golang.org/cl/6903048

diff --git a/doc/go_spec.html b/doc/go_spec.html
index 6e88d47f31458195db42f5463c008e27e8b5776f..468fb3ad2876de91b68fa7d98a79331650cec23d 100644 (file)
--- a/doc/go_spec.html
+++ b/doc/go_spec.html
@@ -1,6 +1,6 @@
 <!--{
        "Title": "The Go Programming Language Specification",
-       "Subtitle": "Version of December 10, 2012",
+       "Subtitle": "Version of December 12, 2012",
        "Path": "/ref/spec"
 }-->
 
@@ -815,12 +815,13 @@ ElementType = Type .
 </pre>
 
 <p>
-The length is part of the array's type and must be a
-<a href="#Constant_expressions">constant expression</a> that evaluates to a non-negative
-integer value.  The length of array <code>a</code> can be discovered
+The length is part of the array's type; it must evaluate to a non-
+negative <a href="#Constants">constant</a> representable by a value
+of type <code>int</code>.
+The length of array <code>a</code> can be discovered
 using the built-in function <a href="#Length_and_capacity"><code>len</code></a>.
 The elements can be addressed by integer <a href="#Index_expressions">indices</a>
-indices 0 through <code>len(a)-1</code>.
+0 through <code>len(a)-1</code>.
 Array types are always one-dimensional but may be composed to form
 multi-dimensional types.
 </p>
@@ -2497,13 +2498,21 @@ The value <code>x</code> is called the
 rules apply:
 </p>
 
+<p>
+If <code>a</code> is not a map:
+</p>
+<ul>
+       <li>the index <code>x</code> must be an integer value; it is <i>in range</i> if <code>0 &lt;= x &lt; len(a)</code>,
+           otherwise it is <i>out of range</i></li>
+       <li>a <a href="#Constants">constant</a> index must be non-negative
+            and representable by a value of type <code>int</code>
+</ul>
+
 <p>
 For <code>a</code> of type <code>A</code> or <code>*A</code>
 where <code>A</code> is an <a href="#Array_types">array type</a>:
 </p>
 <ul>
-       <li><code>x</code> must be an integer value; it is <i>in range</i> if <code>0 &lt;= x &lt; len(a)</code>,
-           otherwise it is <i>out of range</i></li>
        <li>a <a href="#Constants">constant</a> index must be in range</li>
        <li>if <code>a</code> is <code>nil</code> or if <code>x</code> is out of range at run time,
            a <a href="#Run_time_panics">run-time panic</a> occurs</li>
@@ -2515,9 +2524,6 @@ where <code>A</code> is an <a href="#Array_types">array type</a>:
 For <code>a</code> of type <code>S</code> where <code>S</code> is a <a href="#Slice_types">slice type</a>:
 </p>
 <ul>
-       <li><code>x</code> must be an integer value; it is <i>in range</i> if <code>0 &lt;= x &lt; len(a)</code>,
-           otherwise it is <i>out of range</i></li>
-       <li>a <a href="#Constants">constant</a> index must not be negative</li>
        <li>if the slice is <code>nil</code> or if <code>x</code> is out of range at run time,
            a <a href="#Run_time_panics">run-time panic</a> occurs</li>
        <li><code>a[x]</code> is the slice element at index <code>x</code> and the type of
@@ -2529,9 +2535,7 @@ For <code>a</code> of type <code>T</code>
 where <code>T</code> is a <a href="#String_types">string type</a>:
 </p>
 <ul>
-       <li><code>x</code> must be an integer value; it is <i>in range</i> if <code>0 &lt;= x &lt; len(a)</code>,
-           otherwise it is <i>out of range</i></li>
-       <li>a <a href="#Constants">constant</a> index must not be negative, and it must be in range
+       <li>a <a href="#Constants">constant</a> index must be in range
            if the string <code>a</code> is also constant</li>
        <li>if <code>x</code> is out of range at run time,
            a <a href="#Run_time_panics">run-time panic</a> occurs</li>
@@ -2635,7 +2639,9 @@ For arrays or strings, the indices <code>low</code> and <code>high</code> are
 <i>in range</i> if <code>0 &lt;= <code>low</code> &lt;= <code>high</code> &lt;= len(a)</code>,
 otherwise they are <i>out of range</i>.
 For slices, the upper index bound is the slice capacity <code>cap(a)</code> rather than the length.
-A <a href="#Constant_expressions">constant</a> index must not be negative, and if both indices
+A <a href="#Constants">constant</a> index must be non-negative and representable by a value of type
+<code>int</code>.
+If both indices
 are constant, they must satisfy <code>low &lt;= high</code>. If <code>a</code> is <code>nil</code>
 or if the indices are out of range at run time, a <a href="#Run_time_panics">run-time panic</a> occurs.
 </p>
@@ -4985,8 +4991,9 @@ make(T, n)       channel    asynchronous channel of type T, buffer size n
 
 <p>
 The size arguments <code>n</code> and <code>m</code> must be integer values.
-A <a href="#Constants">constant</a> size argument must not be negative, and
-if both <code>n</code> and <code>m</code> are provided and are constant, then
+A <a href="#Constants">constant</a> size argument must be non-negative and
+representable by a value of type <code>int</code>.
+If both <code>n</code> and <code>m</code> are provided and are constant, then
 <code>n</code> must be no larger than <code>m</code>.
 If <code>n</code> is negative or larger than <code>m</code> at run time,
 a <a href="#Run_time_panics">run-time panic</a> occurs.
@@ -4995,6 +5002,7 @@ a <a href="#Run_time_panics">run-time panic</a> occurs.
 <pre>
 s := make([]int, 10, 100)       // slice with len(s) == 10, cap(s) == 100
 s := make([]int, 1e3)           // slice with len(s) == cap(s) == 1000
+s := make([]int, 1&lt;&lt;63)         // illegal: len(s) is not representable by a value of type int
 s := make([]int, 10, 0)                // illegal: len(s) > cap(s)
 c := make(chan int, 10)         // channel with a buffer size of 10
 m := make(map[string]int, 100)  // map with initial space for 100 elements