evnu
Map.new/2 uses :lists.reverse/1
While scrolling around, I found that Map.new/2 uses :lists.reverse/1 after the transformation on the enumerable is completed. I wonder if that is actually needed. I benchmarked the implementation against one without :lists.reverse/1 with benchee. The results are that it doesn’t slow down the function, but memory usage increases. I guess one reason to use :lists.reverse/1 is in order to handle duplicate keys just as Map.new/1 does. Is that the reason why :lists.reverse/1 is used?
Marked As Solved
NobbZ
:lists.reverse/1 is used to make sure that elements are inserted in order.
[1, 2, 2, 3, 4] |> Enum.with_index |> Map.new(&(&1))
The snippet above will cause different results between reversing the acc and not reversing it.
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benwilson512
This is the reason yes.
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