vec( $_, $offset, $size ) = 1 for substr( $astring, $start, $len ); has no big advantage over vec( substr( $astring, $start, $len ), $offset, $size ) = 1;

I agree. But I've only very recently 'discovered' nested lvalue subs -- this thread is the first time I've ever used the construct publicly -- and I've never seen it used anywhere else.

I can well imagine that there are lot of silent readers looking at

• vec( vec( ... ), ... ) = 1;
• vec( substr(... ), ... ) = 1;
• substr( vec( ... ), ... ) = $stuff;
• substr( substr( ...), ... ) = $stuff;
• substr( vec( substr( vec( substr( ...), ... ), ... ), ... ), ... ) = $something;

and thinking:

"I'd never use such an unholy constructs even if it meant my code running a 1000 times more slowly."