spec: document the new unsafe functions SliceData, String, and StringData

For #53003.

Change-Id: If5d76c7b8dfcbcab919cad9c333c0225fc155859
Reviewed-on: https://go-review.googlesource.com/c/go/+/449537
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@google.com>

diff --git a/doc/go_spec.html b/doc/go_spec.html
index e55f34aa6383019530846849198b8fdac7fa8a8d..3dcab9c4a6e5181326124f6219665956d5f99bed 100644 (file)
--- a/doc/go_spec.html
+++ b/doc/go_spec.html
@@ -8006,6 +8006,9 @@ func Sizeof(variable ArbitraryType) uintptr
 type IntegerType int  // shorthand for an integer type; it is not a real type
 func Add(ptr Pointer, len IntegerType) Pointer
 func Slice(ptr *ArbitraryType, len IntegerType) []ArbitraryType
+func SliceData(slice []ArbitraryType) *ArbitraryType
+func String(ptr *byte, len IntegerType) string
+func StringData(str string) *byte
 </pre>
 
 <!--
@@ -8109,6 +8112,27 @@ or if <code>ptr</code> is <code>nil</code> and <code>len</code> is not zero,
 a <a href="#Run_time_panics">run-time panic</a> occurs.
 </p>
 
+<p>
+The function <code>SliceData</code> returns a pointer to the underlying array of the <code>slice</code> argument.
+If the slice's capacity <code>cap(slice)</code> is not zero, that pointer is <code>&slice[:1][0]</code>.
+If <code>slice</code> is <code>nil</code>, the result is <code>nil</code>.
+Otherwise it  is a non-<code>nil</code> pointer to an unspecified memory address.
+</p>
+
+<p>
+The function <code>String</code> returns a <code>string</code> value whose underlying bytes start at
+<code>ptr</code> and whose length is <code>len</code>.
+The same requirements apply to the <code>ptr</code> and <code>len</code> argument as in the function
+<code>Slice</code>. If <code>len</code> is zero, the result is the empty string <code>""</code>.
+Since Go strings are immutable, the bytes passed to <code>String</code> must not be modified afterwards.
+</p>
+
+<p>
+The function <code>StringData</code> returns a pointer to the underlying bytes of the <code>str</code> argument.
+For an empty string the return value is unspecified, and may be <code>nil</code>.
+Since Go strings are immutable, the bytes returned by <code>StringData</code> must not be modified.
+</p>
+
 <h3 id="Size_and_alignment_guarantees">Size and alignment guarantees</h3>
 
 <p>