No overload matches with subtype

[teodor-pripoae]

Hi

I have the following code:

require "json"

def test_method(ids : Array(String), options : Hash(String, JSON::Type))
  options.merge({"ids": ids})
end

puts test_method(["123", "456"], {"asdf": "foo", "data": {"a": "b"}})

Since Hash(String, Hash(String, String) | String) is a subtype permitted by JSON::Type, it should work.

I'm getting this error:

Error in ./test.cr:7: no overload matches 'test_method' with types Array(String), Hash(String, Hash(String, String) | String)
Overloads are:
 - test_method(ids : Array(String), options : Hash(String, JSON::Type))

puts test_method(["123", "456"], {"asdf": "foo", "data": {"a": "b"}})

[asterite]

The answer is: it depends.

Consider this:

def foo(x : Array(String | Int32))
end

a = Array(Int32).new
foo(a)

Should it compile? Well, if we only read from x then the answer is yes. If we write to x then probably no (we wouldn't want to insert a string inside an array of ints).

There's a tracking issue for covariance and contravariance, #1297. I'll close this in favor of that one. Until we resolve what to do with this no sane behaviour can be expected from this. Your best option right now is to either don't use a type annotation, or type the hash as the property type:

require "json"

def test_method(ids, options)
  options.merge({"ids": ids})
end

puts test_method(["123", "456"], {"asdf": "foo", "data": {"a": "b"}})

require "json"

def test_method(ids : Array(JSON::Type), options : Hash(String, JSON::Type))
  options.merge({"ids": ids} of String => JSON::Type)
end

puts test_method(
  ["123", "456"] of JSON::Type,
  {
    "asdf": "foo" as JSON::Type,
    "data": {"a": "b"} of String => JSON::Type,
  } of String => JSON::Type)