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Comment by 2h | Hacker News Reader

> a, b = b, a

> (don't know why this is so famous, I never, ever used that in prod)

This allows you to sort an array in place. It's heavily used in Go:

A variant is useful to update two (or more) dependent variables in one go without having to introduce temporary variables. For example to calculate the greatest common divisor using the Euclidean algorithm:

    def gcd(a, b):
        while b > 0:
            a, b = b, a % b
        return a

Swapping variables around is also really handy for patterns like "alter list a until stable", especially with the walrus := operator allowing you to avoid declaring b outside of the while loop, keeping the intent clearer.

Yeah but in Python list.sort() takes care of that.

True, but every once in a while we want to sort something that isn't a list and/or with a custom sorting algorithm.

You can always write something like {var tmp=a;a=b;b=tmp;} in any language if you want to sort in place.

> in place

that doesn't mean what you think it means.

Do you know what it means? It seems irrelevant to the discussion, introducing a new variable won't make you unable to sort in place. You could even allocate memory on the heap and still sort in place.

> Do you know what it means?

yeah, it means no temporary variable.

No, it means the original data structure gets modified. In this example, the contents of the array you pass to the sort function will be sorted, without copying to a new array. Some overhead is acceptable, if only because you need loop counters.

What I find interesting is that you call someone out on not knowing a term, then you're being called out, then you respond claiming you know the term and explain the term… And at no point did it occur to you to actually duckduckgo it and make sure you're correct.

If you're creating a new variable with allocated memory, your process is no longer "in place". Sorry I didn't graduate from the school of duckduckgo like you did, instead I studied the language specification.

Apparently they taught you there to never verify your knowledge not even if multiple other people point out you're wrong. A strong, religious-like conviction is all you need, it's not like you could possibly be in error. Of course a web search engine cannot lead to valuable information, therefore it is reasonable to ridicule anyone who uses it.

The difference here is, a,b=b,a will use one less bytecode, by taking advantage of ROT_TWO

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