It is my understanding that for the purposes of efficiency, the actual opcodes that constitute a statement like ++$i can be split up in expressions like this. Possible example: the value of $i is fetched, incremented, then other (unrelated) opcodes are done, then finally the new value is placed in $i.

The expressions that constitute the arguments are no longer atomic transactions! That would explain why in these cases you can sometimes even get behavior that differs from any execution order (at least, any that evaluates arguments atomically).

I could be totally off-base here, but maybe some perlgutsgeek can authoritatively clarify the situation.

---

---

• Are you posting in the right place? Check out Where do I post X? to know for sure.
• Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:

  <code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>

• Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
• Want more info? How to link or How to display code and escape characters are good places to start.