埃菲尔铁塔：最好的方式来比较类型而不会引起嘘声

Question

有一个 Catcall 试图比较 2 种类型，我该怎么做才能避免通过另一个非专用方法（例如字符串、class_id 或类似的东西）？

SIT_UTIL

    class_name_lowercase (a_string: STRING): STRING
            -- a copy lowercased and pruned from preceding '!'
        do
            Result := a_string
            if Result.index_of('!', 1) = 1 then
                Result := Result.substring (2, Result.count)
                Result.to_lower
            else
                Result := Result.as_lower
            end
        ensure
            instance_free: class
        end

CLIENT_CLASS

    relationship_from_secondary_type_equal (a_type: like relationships.item.secondary_type): detachable like relationships.item
            -- Returns first instance of found relationship secondary type which equals given one
        do
            across
                relationships as l_rel
            until
                Result /= Void
            loop
--              if attached (a_type / l_rel.item.secondary_type) then -- Don't want conformance but equality

--              if attached (a_type.is_equal (l_rel.item.secondary_type)) then -- tried but as is_equal needs a like Current => Catcall
--              if attached (a_type.equal (a_type, l_rel.item.secondary_type)) then -- Catcall because b signature is like a
                if {SIT_UTIL}.class_name_lowercase (a_type).is_equal({SIT_UTIL}.class_name_lowercase (l_rel.item.secondary_type)) then
                    Result := l_rel.item
                end
            end
            check
                not_found_relationship: Result /= Void
            end
        end

Answer 1

一致性属性是反对称的，即如果A→B和B→A，那么 A = B。因此，两种类型是相等的，它们相互符合：

    a_type.conforms_to (l_rel.item.secondary_type) and
    l_rel.item.secondary_type.conforms_to (a_type)

(尽管 conforms_to 比较的是对象的类型而不是对象本身，但是上面的表达式仍然可以，因为由于一致性规则 A = B 当且仅当如果 TYPE [A] = TYPE [B] 当 A 和 B 本身就是类型。）

如果其中一种类型是附加的，另一种是可拆卸的，您仍然可能希望将它们作为相等进行比较。在这种情况下，可以使用以下代码：

    is_conforming (a_type, l_rel.item.secondary_type) and
    is_conforming (l_rel.item.secondary_type, a_type)

比较谓词忽略附件标记的地方：

is_conforming (t1, t2: TYPE [detachable ANY]): BOOLEAN
  do
    Result :=
      ({REFLECTOR}.type_of_type ({REFLECTOR}.detachable_type (t1.type_id))).conforms_to
      ({REFLECTOR}.type_of_type ({REFLECTOR}.detachable_type (t2.type_id)))
  end

埃菲尔铁塔：最好的方式来比较类型而不会引起嘘声

Eiffel: best way to compare types without getting a catcall

eiffel

SIT_UTIL

CLIENT_CLASS