add a reminder comment about strings' immutability

1 files changed, 8 insertions, 1 deletions

diff --git a/str.h b/str.h
index 1969d6b..33decac 100644
--- a/str.h
+++ b/str.h
@@ -1,11 +1,16 @@
 #ifndef STR_H
 #define STR_H
 
-#include <string.h>
 #include <stddef.h>
 
 #include "arena.h"
 
+/* non-const *s for convenience's sake, but strings should
+ * be treated as immutable unless absolutely certain there
+ * are no dangling references to substrings concatenated
+ * into it (because str_cat() is sometimes in-place).
+ */
+
 typedef struct {
 	char *s;
 	ptrdiff_t n;
@@ -43,6 +48,8 @@ Str str_replace_end(Str s, Str a, Str b, Arena *m);
 
 #ifdef STR_IMPL
 
+#include <string.h>
+
 /* conversions */
 
 Str str_from_cstr(const char *s) {