Combine

README.md

@@ -116,6 +116,19 @@ when None
 end
 ```
 
+## `combine([maybes])`
+
+With `combine` you can create a new `Maybe` which includes an array of values from combined `Maybe`s. If any of the combined `Maybe`s is a `None`, a `None` will be returned.
+
+```
+mparams = Maybe(params)
+
+duration = Maybe
+  .combine(mparams[:start_date], mparams[:end_date])
+  .map { |(start, end)| Date.parse(end) - Date.parse(start) }
+  .get_or_else "Unknown"
+```
+
 ## Examples
 
 Instead of using if-clauses to define whether a value is a `nil`, you can wrap the value with `Maybe()` and threat it the same way whether or not it is a `nil`

lib/possibly.rb

@@ -15,6 +15,19 @@ def ==(other)
     other.class == self.class
   end
   alias_method :eql?, :==
+
+  def combine(*maybes)
+    Maybe.combine(self, *maybes)
+  end
+
+  def self.combine(*maybes)
+    if maybes.any?(&:is_none?)
+      None()
+    else
+      values = maybes.map(&:get)
+      Maybe(values)
+    end
+  end
 end
 
 # Represents a non-empty value

spec/spec.rb

@@ -156,4 +156,22 @@ def test_case_when(case_value, match_value, non_match_value)
       expect(Some([1, 2, 3]).map { |arr| arr.map { |v| v * v } }.get).to eql([1, 4, 9])
     end
   end
-end
+
+  describe "combine" do
+    it "combines multiple Some values" do
+      expect(Maybe("foo").combine(Maybe("bar")).get).to eql(["foo", "bar"])
+      expect(Maybe("foo").combine(Maybe("bar"), Maybe("baz")).get).to eql(["foo", "bar", "baz"])
+      expect(Maybe.combine(Maybe("foo"), Maybe("bar"), Maybe("baz")).get).to eql(["foo", "bar", "baz"])
+      expect(Maybe.combine(Maybe("foo"), Maybe("bar"), Maybe("baz")).map do |(foo, bar, baz)|
+        "#{foo} and #{bar} and finally, #{baz}"
+      end.get).to eql ("foo and bar and finally, baz")
+    end
+
+    it "returns None if any None" do
+      expect(Maybe("foo").combine(Maybe(nil)).or_else { false }).to eql(false)
+      expect(Maybe("foo").combine(Maybe(nil)) { |a, b| "#{a} + #{b}" }.or_else { false }).to eql(false)
+      expect(Maybe.combine(Maybe("foo"), Maybe(nil)).or_else { false }).to eql(false)
+      expect(Maybe.combine(Maybe("foo"), Maybe(nil)) { |a, b| "#{a} + #{b}" }.or_else { false }).to eql(false)
+    end
+  end
+end