Array: optimize shift and unshift

etc/lldb/crystal_formatters.py

@@ -11,7 +11,7 @@ def update(self):
             self.valobj = self.valobj.Dereference()
         self.size = int(self.valobj.child[0].value)
         self.type = self.valobj.type
-        self.buffer = self.valobj.child[2]
+        self.buffer = self.valobj.child[3]
 
     def num_children(self):
         size = 0 if self.size is None else self.size

spec/std/array_spec.cr

@@ -389,6 +389,15 @@ describe "Array" do
       a.should eq([6, 7, 4, 5])
     end
 
+    it "optimizes when index is 0" do
+      a = [1, 2, 3, 4, 5, 6, 7, 8]
+      buffer = a.@buffer
+      a[0..2] = 10
+      a.should eq([10, 4, 5, 6, 7, 8])
+      a.@offset_to_buffer.should eq(2)
+      a.@buffer.should eq(buffer + 2)
+    end
+
     it "replaces entire range with a value for empty array (#8341)" do
       a = [] of Int32
       a[..] = 6
@@ -535,6 +544,15 @@ describe "Array" do
       a.should eq([1, 3, 4])
     end
 
+    it "deletes at beginning is same as shift" do
+      a = [1, 2, 3, 4]
+      buffer = a.@buffer
+      a.delete_at(0)
+      a.should eq([2, 3, 4])
+      a.@offset_to_buffer.should eq(1)
+      a.@buffer.should eq(buffer + 1)
+    end
+
     it "deletes use range" do
       a = [1, 2, 3]
       a.delete_at(1).should eq(2)
@@ -1173,6 +1191,101 @@ describe "Array" do
         a.shift(-1)
       end
     end
+
+    it "shifts one and resizes" do
+      a = [1, 2, 3, 4]
+      old_capacity = a.@capacity
+      a.shift.should eq(1)
+      a.@offset_to_buffer.should eq(1)
+      a << 5
+      a.@capacity.should eq(old_capacity * 2)
+      a.@offset_to_buffer.should eq(1)
+      a.size.should eq(4)
+      a.should eq([2, 3, 4, 5])
+    end
+
+    it "shifts almost all and then avoid resize" do
+      a = [1, 2, 3, 4]
+      old_capacity = a.@capacity
+      (1..3).each do |i|
+        a.shift.should eq(i)
+      end
+      a.@offset_to_buffer.should eq(3)
+      a << 5
+      a.@capacity.should eq(old_capacity)
+      a.@offset_to_buffer.should eq(0)
+      a.size.should eq(2)
+      a.should eq([4, 5])
+    end
+
+    it "shifts and then concats Array" do
+      size = 10_000
+      a = (1..size).to_a
+      (size - 1).times do
+        a.shift
+      end
+      a.size.should eq(1)
+      a.concat((1..size).to_a)
+      a.size.should eq(size + 1)
+      a.should eq([size] + (1..size).to_a)
+    end
+
+    it "shifts and then concats Enumerable" do
+      size = 10_000
+      a = (1..size).to_a
+      (size - 1).times do
+        a.shift
+      end
+      a.size.should eq(1)
+      a.concat((1..size))
+      a.size.should eq(size + 1)
+      a.should eq([size] + (1..size).to_a)
+    end
+
+    it "shifts all" do
+      a = [1, 2, 3, 4]
+      buffer = a.@buffer
+      4.times do
+        a.shift
+      end
+      a.size.should eq(0)
+      a.@offset_to_buffer.should eq(0)
+      a.@buffer.should eq(buffer)
+    end
+
+    it "shifts all after pop" do
+      a = [1, 2, 3, 4]
+      buffer = a.@buffer
+      a.pop
+      3.times do
+        a.shift
+      end
+      a.size.should eq(0)
+      a.@offset_to_buffer.should eq(0)
+      a.@buffer.should eq(buffer)
+    end
+
+    it "pops after shift" do
+      a = [1, 2, 3, 4]
+      buffer = a.@buffer
+      3.times do
+        a.shift
+      end
+      a.pop
+      a.size.should eq(0)
+      a.@offset_to_buffer.should eq(0)
+      a.@buffer.should eq(buffer)
+    end
+
+    it "shifts all with shift(n)" do
+      a = [1, 2, 3, 4]
+      buffer = a.@buffer
+      a.shift
+      a.shift(3)
+      a.size.should eq(0)
+      a.@offset_to_buffer.should eq(0)
+      a.@buffer.should eq(buffer)
+    end
   end
 
   describe "shuffle" do
@@ -1441,6 +1554,22 @@ describe "Array" do
       a.should eq [3, 1, 2]
     end
 
+    it "unshifts one elements three times" do
+      a = [] of Int32
+      3.times do |i|
+        a.unshift(i)
+      end
+      a.should eq([2, 1, 0])
+    end
+
+    it "unshifts one element multiple times" do
+      a = [1, 2]
+      (3..100).each do |i|
+        a.unshift(i)
+      end
+      a.should eq((3..100).to_a.reverse + [1, 2])
+    end
+
     it "unshifts multiple elements" do
       a = [1, 2]
       a.unshift(3, 4).should be(a)
@@ -1452,6 +1581,26 @@ describe "Array" do
       a.unshift(1, 2, 3).should be(a)
       a.should eq([1, 2, 3])
     end
+
+    it "unshifts after shift" do
+      a = [1, 2, 3, 4]
+      buffer = a.@buffer
+      a.shift
+      a.unshift(10)
+      a.should eq([10, 2, 3, 4])
+      a.@offset_to_buffer.should eq(0)
+      a.@buffer.should eq(buffer)
+    end
+
+    it "unshifts many after many shifts" do
+      a = [1, 2, 3, 4, 5, 6, 7, 8]
+      buffer = a.@buffer
+      3.times { a.shift }
+      a.unshift(10, 20, 30)
+      a.should eq([10, 20, 30, 4, 5, 6, 7, 8])
+      a.@offset_to_buffer.should eq(0)
+      a.@buffer.should eq(buffer)
+    end
   end
 
   it "does update" do