Add Map.intersect/2 and Map.intersect/3

[ed-flanagan]

Following up from https://elixirforum.com/t/map-intersection-2/53121/12. I didn't see any duplicates, hopefully it's okay I pushed up.

My first PR, so tried to follow https://github.com/elixir-lang/elixir#contributing & https://github.com/elixir-lang/elixir/blob/main/CODE_OF_CONDUCT.md as best as I could.

---

• Add corresponding functions for Erlang's :maps.intersect/2 & :maps.intersect_with/3.
• Largely cargo-culted from Map.merge/3, including the tests & docs. More than happy to extend these.
• I extended the diff list in KeywordTest since I wasn't sure if extending Keyword would be out-of-scope. Happy to add a Keyword.intersect function as well, if desired.
• make test_stdlib resulted in 1948 doctests, 4187 tests, 0 failures, 13 excluded
• Test from running ./bin/iex

  ❯ ./bin/iex
  Erlang/OTP 25 [erts-13.1.3] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [jit] [dtrace]
  
  Interactive Elixir (1.15.0-dev) - press Ctrl+C to exit (type h() ENTER for help)
  iex(1)> Map.intersect(%{a: 1, b: 2}, %{b: 2, c: 3})
  %{b: 2}
  iex(2)> Map.intersect(%{a: 1, b: 2}, %{b: 2, c: 3}, fn _k, v1, v2 -> v1 + v2 end)
  %{b: 4}
  

[adamu]

This is not the case, right?

[ed-flanagan]

What exactly?

map1), and value2 (the value of key in map2). The value returned by
fun is used as the value under key in the resulting map.

I tried to adapt the same wording used in Map.merge, akin to https://www.erlang.org/doc/man/maps.html#intersect_with-3.

Inlined by the compiler.

I cargo-culted this since other functions that just pass to Erlang functions included it (even without defdelegate). E.g.

elixir/lib/elixir/lib/map.ex

Line 275 in bc0cf0b

def has_key?(map, key), do: :maps.is_key(key, map)

or

elixir/lib/elixir/lib/map.ex

Line 388 in bc0cf0b

:maps.update(key, value, map)

. But I'm not entirely sure, happy to remove

[leandrocp]

AFAIK you'd have to add the inline rules at https://github.com/elixir-lang/elixir/blob/main/lib/elixir/src/elixir_rewrite.erl, which I believe is expected in this case.

[stevensonmt]

I would prefer documentation use language based on the Elixir MapSet documentation rather than the Erlang :maps docs. For example MapSet.intersection/2 docs include

Returns a set containing only members that map_set1 and map_set2 have in common.

This is much nicer than

Intersects two sets into one.

[whatyouhide]

Fantastic!

[josevalim]

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