[Proposal] operator =~ should support maps

[jer...@companykitchen.com]

I think it would be useful if =~ supported maps.  =~ would return true if the key/values in the right hand map were also contained in the left-hand map.  I think this would be especially useful for testing, as you could check that the result matched a subset of the map, rather than the whole map.

e.g.

data = Repo.insert!(src)

# data = %Data{id: 25, field1: "foo", field2: "bar", inserted_at: ~N[2017-01-01], updated_at: ~N[2017-01-01]}

assert data =~ %{field1: "foo", field2: "bar"}  # true

[Andrew Timberlake]

You can do that with pattern matching,

assert %{field1: "foo", field2: "bar"} = data

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[jer...@companykitchen.com]

Yes, but that throws a MatchError exception if not satisfied, not a true/false.  Ideally, in the assertion results, it would highlight the failing key/values as well.  Primarily for testing, but also a quick way to test for the presence of multiple key/values in larger maps.

[Louis Pilfold]

Hey

The `assert` macro handles MatchError as well as true/false.

>  Ideally, in the assertion results, it would highlight the failing key/values as well.

This would be a nice addition to ExUnit. I would rather see this than any addition to =~

Cheers,

Louis

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[jer...@companykitchen.com]

Wouldn't it be more difficult to determine the right thing to print based on a MatchError, than the operator and operands?  Maybe not all that harder, but I do prefer the explicitness of saying "I'm comparing a subset", rather than "attempting an assignment" 

[Allen Madsen]

If you want a boolean value for a match, you can use: https://hexdocs.pm/elixir/Kernel.html#match?/2

Allen Madsen
http://www.allenmadsen.com

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[José Valim]

Use match?/2:

assert match?(%{field1: "foo", field2: "bar"}, data)

The operator =~ was designed to focus exclusively on strings and we don't plan to relax those constraints.

José Valim

www.plataformatec.com.br

Founder and 

Director of R&D

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[jer...@companykitchen.com]

What would you all think of changing the assert output when the argument to assert is match?(map, map) so that it shows the difference similar to if we did an ==, except the extra fields in the right-hand map would be omitted?  This is what we currently see when using "assert match?(%{field1: "foo", field2: "bar"}, data)":

  1) test map1 (MapPropsalTest)

     test/map_propsal_test.exs:10

     match (match?) failed

     code:  assert match?(%{field1: "foo", field2: "bar", field3: "not-there"}, map)

     right: %{

              field1: "foo",

              field2: "bar",

              inserted_at: ~N[2017-10-19 02:10:25.254692]

            }

     stacktrace:

       test/map_propsal_test.exs:12: (test)

How I think it should read instead when the args to match? are both maps :

  2) test map2 (MapPropsalTest)

     test/map_propsal_test.exs:15

     match (match?) failed

     code:  assert match?(%{field1: "foo", field2: "bar", field3: "not-there"}, map)

     left:  %{field1: "foo", field2: "bar", <red>field3: "not-there"</red>}

     right: %{field1: "foo", field2: "bar"}

     stacktrace:

       test/map_propsal_test.exs:17: (test)

I'd be happy to do the work.

[José Valim]

There is already an open issue for that in the form of doing something similar for assert_receive but that's actually very complex since the left side is a *pattern* and not a value. So we would need to have a "pattern evaluator" or similar.

José Valim

www.plataformatec.com.br

Founder and 

Director of R&D

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