cache: move doc to cache.h

[thirdparty/git.git] / cache.h

diff --git a/cache.h b/cache.h
index 04cabaac119540e89f58cd91c46b17ddb30a26ce..8fbbdf971a3789287f1fa625cf43f46e2b56b282 100644 (file)
--- a/cache.h
+++ b/cache.h
@@ -632,10 +632,43 @@ int daemonize(void);
 
 #define alloc_nr(x) (((x)+16)*3/2)
 
-/*
- * Realloc the buffer pointed at by variable 'x' so that it can hold
- * at least 'nr' entries; the number of entries currently allocated
- * is 'alloc', using the standard growing factor alloc_nr() macro.
+/**
+ * Dynamically growing an array using realloc() is error prone and boring.
+ *
+ * Define your array with:
+ *
+ * - a pointer (`item`) that points at the array, initialized to `NULL`
+ *   (although please name the variable based on its contents, not on its
+ *   type);
+ *
+ * - an integer variable (`alloc`) that keeps track of how big the current
+ *   allocation is, initialized to `0`;
+ *
+ * - another integer variable (`nr`) to keep track of how many elements the
+ *   array currently has, initialized to `0`.
+ *
+ * Then before adding `n`th element to the item, call `ALLOC_GROW(item, n,
+ * alloc)`.  This ensures that the array can hold at least `n` elements by
+ * calling `realloc(3)` and adjusting `alloc` variable.
+ *
+ * ------------
+ * sometype *item;
+ * size_t nr;
+ * size_t alloc
+ *
+ * for (i = 0; i < nr; i++)
+ *     if (we like item[i] already)
+ *             return;
+ *
+ * // we did not like any existing one, so add one
+ * ALLOC_GROW(item, nr + 1, alloc);
+ * item[nr++] = value you like;
+ * ------------
+ *
+ * You are responsible for updating the `nr` variable.
+ *
+ * If you need to specify the number of elements to allocate explicitly
+ * then use the macro `REALLOC_ARRAY(item, alloc)` instead of `ALLOC_GROW`.
  *
  * Consider using ALLOC_GROW_BY instead of ALLOC_GROW as it has some
  * added niceties.