note TheDamian <blockquote><i> ...one of the MTOW you promote TDI is, if not wrong, then sub-optimal </i></blockquote> <p>One of the points I make in PBP is that "sub-optimal" is not a easy thing to judge as soon as you have more than one metric to optimize. PBP suggests at least four: maintainability, robustness, performance, and conciseness (and argues that that is the approximate order of importance of the four). <p>The recommendation to use anonymous hashes when passing one-off argument lists trades a little less performance for a little more conciseness, some improved robustness, and (if used consistently throughout the code) better maintainability. <p>Of course, you're perfectly correct to factor out the hash memory reallocations into a single declaration if you're going to repeat the same call hundreds (or millions) of times, but as a default habit, just building an anonymous hashref at the point you need it is cleaner, less error prone, and more concise. And the performance cost on a single call at modern processor speeds isn't worth the hassle of coordinating between separate hash declarations and uses. <p>All of which is why inlined hashes were the default recommendation in PBP. <p>PS: You also asked what worse mistakes I made in PBP. One of them was not finding a way to adequately get across that the advice in the book is meant to be a starting point, a default zero-state, an initiator of conscious thought, rather than an end-point of discussion. Gods know, I <i>tried</i> to convey that (devoting most of the first chapter to the idea), but I stupidly didn't put any code in that chapter, so most readers just seem to skip straight over it. :-( 766188 766912