MT#7679 utils: add table.shift()

ngcp/utils.lua

@@ -120,6 +120,40 @@ function table.shuffle(tab)
   return res
 end
 
+-- range(start)             returns an iterator from 1 to a (step = 1)
+-- range(start, stop)       returns an iterator from a to b (step = 1)
+-- range(start, stop, step) returns an iterator from a to b, counting by step.
+range = function (i, to, inc)
+  -- range(--[[ no args ]]) -> return "nothing" to fail the loop in the caller
+  if i == nil then return end
+
+  if not to then
+     to = i
+     i  = to == 0 and 0 or (to > 0 and 1 or -1)
+  end
+
+  -- we don't have to do the to == 0 check
+  -- 0 -> 0 with any inc would never iterate
+  inc = inc or (i < to and 1 or -1)
+
+  -- step back (once) before we start
+  i = i - inc
+
+  return function () if i == to then return nil end i = i + inc return i, i end
+end
+
+function table.shift(t, positions)
+  local k, v
+  local res = {}
+  for k in range(1, positions % #t) do
+    v = table.remove(t, k-#res)
+    table.insert(res, v)
+  end
+  for _,v in ipairs(res) do
+    table.insert(t, v)
+  end
+end
+
 -- from table to string
 -- t = {'a','b'}
 -- implode(",",t,"'")

tests/utils.lua

@@ -73,6 +73,21 @@ TestUtils = {} --class
         assertNotEquals(tmp2, tmp)
     end
 
+    function TestUtils:test_table_shift()
+        assertEquals(self.simple_list, {1,2,3})
+        table.add(self.simple_list, 4)
+        table.add(self.simple_list, 5)
+        table.add(self.simple_list, 6)
+        table.shift(self.simple_list, 2)
+        assertEquals(self.simple_list, {3,4,5,6,1,2})
+    end
+
+    function TestUtils:test_table_shift2()
+        assertEquals(self.simple_list, {1,2,3})
+        table.shift(self.simple_list, 4)
+        assertEquals(self.simple_list, {2,3,1})
+    end
+
     function TestUtils:test_table_tostring()
         assertError(table.tostring,nil)
         assertEquals(table.tostring(self.simple_list), "{1,2,3}")