/* SV* xav_arylen; */
-/* SVpav_REAL is set for all AVs whose xav_array contents are refcounted.
- * Some things like "@_" and the scratchpad list do not set this, to
- * indicate that they are cheating (for efficiency) by not refcounting
- * the AV's contents.
- *
+/* SVpav_REAL is set for all AVs whose xav_array contents are refcounted
+ * and initialized such that any element can be retrieved as a SV*.
+ * Such AVs may be referred to as "real" AVs. Examples include regular
+ * perl arrays, tiedarrays (since v5.16), and padlist AVs.
+ *
+ * Some things do not set SVpav_REAL, to indicate that they are cheating
+ * (for efficiency) by not refcounting the AV's contents or ensuring that
+ * all elements are safe for arbitrary access. This type of AV may be
+ * referred to as "fake" AVs. Examples include "@_" (unless tied), the
+ * scratchpad list, and the backrefs list on an object or stash.
+ *
* SVpav_REIFY is only meaningful on such "fake" AVs (i.e. where SVpav_REAL
* is not set). It indicates that the fake AV is capable of becoming
* real if the array needs to be modified in some way. Functions that
* modify fake AVs check both flags to call av_reify() as appropriate.
*
+ * av_reify() transforms a fake AV into a real one through two actions.
+ * Allocated but unpopulated elements are initialized to make them safe for
+ * arbitrary retrieval and the reference counts of populated elements are
+ * incremented.
+ *
* Note that the Perl stack has neither flag set. (Thus,
* items that go on the stack are never refcounted.)
*
*/
/*
-=for apidoc_section AV Handling
-
=for apidoc ADmnU||Nullav
Null AV pointer.
value of the indices of all the array elements which are currently defined in
C<av>. It does not handle magic, hence the C<p> private indication in its name.
+=for apidoc Am|SV**|AvARRAY|AV* av
+Returns a pointer to the AV's internal SV* array.
+
+This is useful for doing pointer arithmetic on the array.
+If all you need is to look up an array element, then prefer C<av_fetch>.
+
=cut
*/
#define AvREALISH(av) (SvFLAGS(av) & (SVpav_REAL|SVpav_REIFY))
#define AvFILL(av) ((SvRMAGICAL((const SV *) (av))) \
- ? mg_size(MUTABLE_SV(av)) : AvFILLp(av))
+ ? mg_size(MUTABLE_SV(av)) : AvFILLp(av))
#define av_top_index(av) AvFILL(av)
#define av_tindex(av) av_top_index(av)
#define NEGATIVE_INDICES_VAR "NEGATIVE_INDICES"
/*
+
+Note that there are both real and fake AVs; see the beginning of this file and
+'av.c'
+
=for apidoc newAV
+=for apidoc_item newAV_alloc_x
+=for apidoc_item newAV_alloc_xz
+
+These all create a new AV, setting the reference count to 1. If you also know
+the initial elements of the array with, see L</C<av_make>>.
+
+As background, an array consists of three things:
+
+=over
+
+=item 1.
+
+A data structure containing information about the array as a whole, such as its
+size and reference count.
+
+=item 2.
+
+A C language array of pointers to the individual elements. These are treated
+as pointers to SVs, so all must be castable to SV*.
+
+=item 3.
+
+The individual elements themselves. These could be, for instance, SVs and/or
+AVs and/or HVs, etc.
+
+=back
+
+An empty array need only have the first data structure, and all these functions
+create that. They differ in what else they do, as follows:
+
+=over
+
+=item C<newAV> form
-Creates a new AV. The reference count is set to 1.
+=for comment
+'form' above and below is because otherwise have two =items with the same name,
+can't link to them.
-Perl equivalent: C<my @array;>.
+This does nothing beyond creating the whole-array data structure.
+The Perl equivalent is approximately S<C<my @array;>>
+
+This is useful when the minimum size of the array could be zero (perhaps there
+are likely code paths that will entirely skip using it).
+
+If the array does get used, the pointers data structure will need to be
+allocated at that time. This will end up being done by L</av_extend>>,
+either explicitly:
+
+ av_extend(av, len);
+
+or implicitly when the first element is stored:
+
+ (void)av_store(av, 0, sv);
+
+Unused array elements are typically initialized by C<av_extend>.
+
+=item C<newAV_alloc_x> form
+
+This effectively does a C<newAV> followed by also allocating (uninitialized)
+space for the pointers array. This is used when you know ahead of time the
+likely minimum size of the array. It is more efficient to do this than doing a
+plain C<newAV> followed by an C<av_extend>.
+
+Of course the array can be extended later should it become necessary.
+
+C<size> must be at least 1.
+
+=item C<newAV_alloc_xz> form
+
+This is C<newAV_alloc_x>, but initializes each pointer in it to NULL. This
+gives added safety to guard against them being read before being set.
+
+C<size> must be at least 1.
+
+=back
+
+The following examples all result in an array that can fit four elements
+(indexes 0 .. 3):
+
+ AV *av = newAV();
+ av_extend(av, 3);
+
+ AV *av = newAV_alloc_x(4);
+
+ AV *av = newAV_alloc_xz(4);
+
+In contrast, the following examples allocate an array that is only guaranteed
+to fit one element without extending:
+
+ AV *av = newAV_alloc_x(1);
+ AV *av = newAV_alloc_xz(1);
=cut
+
*/
#define newAV() MUTABLE_AV(newSV_type(SVt_PVAV))
+#define newAV_alloc_x(size) av_new_alloc(size,0)
+#define newAV_alloc_xz(size) av_new_alloc(size,1)
/*
* ex: set ts=8 sts=4 sw=4 et:
https://perl5.git.perl.org / perl5.git / blobdiff