I just upgrade OTP to 20.0 and elixir to 1.5.0-rc.1, I got warnings on usage of filter_map. Why is it deprecated?

Changelog for 1.5 says: [Enum] Deprecate Enum.filter_map/3 in favor of Enum.filter/2 + Enum.map/2 or for-comprehensions

Yes, ‘filter+map’ or ‘for’ works, but I want to know the reason behind it.

I think the reason was the fact that it was an outlier. The only “fused” function.

Enum.map_join = Enum.map + Enum.join Enum.flat_map = Enum.map + Enum.concat

Can someone help a rookie (me) understand the […] or for comprehensions component of this deprecation message?

Parsing the English can be odd, but they’re these things, covered in the Guide https://elixir-lang.org/getting-started/comprehensions.html for comprehensions consist of generators and filters, though the filters seem to be less widely known

Here is an example of using comprehension in lieu of Enum.filter_map/3: # filter even numbers filter_fn = fn n -> rem(n, 2) == 0 end # double map_fn = fn n -> n * 2 end some_enum = 1..20 # filter_map version Enum.filter_map(some_enum, filter_fn, map_fn) # comprehension version for n <- some…

[image] michalmuskala: I think the reason was the fact that it was an outlier. The only “fused” function. What about flat_map, flat_map_reduce, map_reduce, map_join and the rest of the “fused” function? Most of them are useful as a way to avoid walking a long list twice.

[image] NobbZ: If you fear multi walks, then use the appropriate Stream functions. So the flat_map, flat_map_reduce, map_reduce and map_join style Enum functions is just a legacy implementation? They don’t give us anything extra, they just help us avoid some extra code for some common use-cas…

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Why Enum.filter_map is deprecated?

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NobbZ October 7, 2017, 10:00am 10

If you fear multi walks, then use the appropriate Stream functions.