Added Enumerable#in_slices_of (#13108)

Co-authored-by: Sijawusz Pur Rahnama <sija@sija.pl>
Co-authored-by: Quinton Miller <nicetas.c@gmail.com>
Co-authored-by: Johannes Müller <straightshoota@gmail.com>

spec/std/enumerable_spec.cr

@@ -569,6 +569,19 @@ describe "Enumerable" do
     end
   end
 
+  describe "in slices of" do
+    it { [1, 2, 3].in_slices_of(1).should eq([[1], [2], [3]]) }
+    it { [1, 2, 3].in_slices_of(2).should eq([[1, 2], [3]]) }
+    it { [1, 2, 3, 4].in_slices_of(3).should eq([[1, 2, 3], [4]]) }
+    it { ([] of Int32).in_slices_of(2).should eq([] of Array(Int32)) }
+
+    it "raises argument error if size is less than 0" do
+      expect_raises ArgumentError, "Size must be positive" do
+        [1, 2, 3].in_slices_of(0)
+      end
+    end
+  end
+
   describe "includes?" do
     it "is true if the object exists in the collection" do
       [1, 2, 3].includes?(2).should be_true

src/enumerable.cr

@@ -629,6 +629,22 @@ module Enumerable(T)
     end
   end
 
+  # Returns an `Array` with chunks in the given size.
+  # Last chunk can be smaller depending on the number of remaining items.
+  #
+  # ```
+  # [1, 2, 3].in_slices_of(2) # => [[1, 2], [3]]
+  # ```
+  def in_slices_of(size : Int) : Array(Array(T))
+    raise ArgumentError.new("Size must be positive") if size <= 0
+
+    ary = Array(Array(T)).new
+    each_slice_internal(size, Array(T), false) do |slice|
+      ary << slice
+    end
+    ary
+  end
+
   # Returns `true` if the collection contains *obj*, `false` otherwise.
   #
   # ```