union, intersection and overlaps? for Ranges

src/range.cr

@@ -252,6 +252,56 @@ struct Range(B, E)
     {% end %}
   end
 
+  # Returns the union of this range, and another.
+  # Returns 0..0 if there is no overlap.
+  #
+  # ```
+  # (1..5).union(5..10)   # => 1..10
+  # (1...10).union(1..10) # => 1..10
+  # ```
+  def union(other : Range)
+    if self.end < other.begin || other.end < self.begin
+      return 0..0
+    end
+
+    larger = (self.end > other.end)
+    if (larger && self.excludes_end?) || (!larger && other.excludes_end?)
+      return (self.begin < other.begin ? self.begin : other.begin)...(self.end > other.end ? self.end : other.end)
+    end
+
+    (self.begin < other.begin ? self.begin : other.begin)..(self.end > other.end ? self.end : other.end)
+  end
+
+  # Returns the intersection of this range, and another.
+  # Returns 0..0 if there is no overlap.
+  #
+  # ```
+  # (2..10).intersection(0..8)   # => 2..8
+  # (1...10).intersection(7..12) # => 7...10
+  # ```
+  def intersection(other : Range)
+    if self.end < other.begin || other.end < self.begin
+      return 0..0
+    end
+
+    larger = (self.end > other.end)
+    if (!larger && self.excludes_end?) || (larger && other.excludes_end?)
+      return (self.begin > other.begin ? self.begin : other.begin)...(self.end < other.end ? self.end : other.end)
+    end
+
+    (self.begin > other.begin ? self.begin : other.begin)..(self.end < other.end ? self.end : other.end)
+  end
+
+  # Returns `true` if this range overlaps with another range.
+  #
+  # ```
+  # (1..10).overlaps?(5..9)    # => true
+  # (1...10).overlaps?(10..11) # => false
+  # ```
+  def overlaps?(other : Range) : Bool
+    !(self.end <= other.begin || other.end <= self.begin)
+  end
+
   # Returns `true` if this range excludes the *end* element.
   #
   # ```