Comment by _delirium | Hacker News Reader

Comment by _delirium | Hacker News Reader

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To me the confusion is more with the loop constructs. My mental model is fine with variable capture in general, but I don't interpret loop variables as "real" variables. What I'd intuitively expect, if I didn't already know that most languages don't do it that way, is that the loop variable is freshly bound on each iteration. That expectation is strengthened by the fact that a lot of languages seem not to want to allow you to actually use it as a real variable anyway: you often can't modify the loop variable within a foreach-style loop, which leads me to view them as fresh immutable bindings per iteration.

Admittedly, the Java for loop is a plain C-style for loop, where you actually can modify the loop variable if you wish, so it pretty much has to work that way. But the binding-reuse behavior of, say, Python's for i in range(n) loop makes less sense to me. IIRC, it's also one of the many contentious differences in Common Lisp between the LOOP and ITERATE macro packages.

Ah yes, it is a problem if a language is not clear about the lifetime semantics of a loop variable.

In Ruby, for example, an idiomatic loop like 10.times{|i| ... } does indeed bind a new variable for every iteration, but that is implicitly clear to anyone with a basic understanding of the language. Likewise, the 3-part for loop of Java et al does not hide the fact that it's the same variable every time through the loop.

The Java for-each loop, on the other hand, is more ambiguous. A quick check seems to indicate that the iterator variable can be declared final and captured in an anonymous inner class. That means that for-each acts differently than for loop and I could see that confusing your average code monkey.

Yeah, I think the main thing that's confusing about the particular example given in this thread is that the common case of looping over integers usually intends a foreach-style loop, but Java syntax doesn't make it easy to do something like for(final int i : Range(1,10)). So people end up using the C-style 3-part for loop when they don't have any real need for its power.

I actually think that will change in Java 7. I will likely not be using "for" very often, and will start using higher-order functions like map and fold. The issue is mainly developers for whom closures are a new concept. If they are too confused as they make their first nervous steps into the world of functional programming, if their first attempts at using closures result in a lot of bugs, then they may write off the whole thing as more complicated than it's worth.

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