Add Enum.[] convenience constructor (#12900)

spec/std/enum_spec.cr

@@ -275,6 +275,32 @@ describe Enum do
     SpecEnum::One.clone.should eq(SpecEnum::One)
   end
 
+  describe ".[]" do
+    it "non-flags enum" do
+      SpecEnum[].should be_nil
+      SpecEnum[One].should eq SpecEnum::One
+      SpecEnum[1].should eq SpecEnum::Two
+      SpecEnum[One, Two].should eq SpecEnum::One | SpecEnum::Two
+      SpecEnum[One, :two].should eq SpecEnum::One | SpecEnum::Two
+      SpecEnum[One, 1].should eq SpecEnum::One | SpecEnum::Two
+    end
+
+    it "flags enum" do
+      SpecEnumFlags.flags.should be_nil
+      SpecEnumFlags[One].should eq SpecEnumFlags::One
+      SpecEnumFlags[2].should eq SpecEnumFlags::Two
+      SpecEnumFlags[One, Two].should eq SpecEnumFlags::One | SpecEnumFlags::Two
+      SpecEnumFlags[One, :two].should eq SpecEnumFlags::One | SpecEnumFlags::Two
+      SpecEnumFlags[One, 2].should eq SpecEnumFlags::One | SpecEnumFlags::Two
+    end
+
+    it "private flags enum" do
+      PrivateFlagsEnum.flags.should be_nil
+      PrivateFlagsEnum[FOO].should eq PrivateFlagsEnum::FOO
+      PrivateFlagsEnum[FOO, BAR].should eq PrivateFlagsEnum::FOO | PrivateFlagsEnum::BAR
+    end
+  end
+
   describe ".flags" do
     it "non-flags enum" do
       SpecEnum.flags.should be_nil

src/enum.cr

@@ -497,12 +497,36 @@ struct Enum
   # ```
   # IOMode.flags(Read, Write) # => IOMode::Read | IOMode::Write
   # ```
+  #
+  # * `Enum.[]` is a more advanced alternative which also allows int and symbol parameters.
   macro flags(*values)
     {% for value, i in values %}\
       {% if i != 0 %} | {% end %}\
       {{ @type }}::{{ value }}{% end %}\
   end
 
+  # Convenience macro to create a combined enum (combines given members using `|` (or) logical operator).
+  #
+  # Arguments can be the name of a member, a symbol representing a member name or a numerical value.
+  #
+  # ```
+  # IOMode[Read]             # => IOMode[Read]
+  # IOMode[1]                # => IOMode[Read]
+  # IOMode[Read, Write]      # => IOMode[Read, Write]
+  # IOMode[Read, 64]         # => IOMode[Read, 64]
+  # IOMode[Read, :write, 64] # => IOMode[Read, Write, 64]
+  # ```
+  macro [](*values)
+    {% for value, i in values %}\
+      {% if i != 0 %} | {% end %}\
+      {% if value.is_a?(Path) %} \
+        {{ @type }}::{{ value }} \
+      {% else %} \
+        {{ @type }}.new({{value}}) \
+      {% end %} \
+    {% end %}\
+  end
+
   # Iterates each member of the enum.
   # It won't iterate the `None` and `All` members of flags enums.
   #