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Task/Queue-Definition/FreeBASIC/queue-definition-1.basic

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+' FB 1.05.0 Win64
+
+' queue_rosetta.bi
+' simple generic Queue type
+
+#Define Queue(T) Queue_##T
+
+#Macro Declare_Queue(T)
+Type Queue(T)
+ Public:
+    Declare Constructor()
+    Declare Destructor()
+    Declare Property capacity As Integer
+    Declare Property count As Integer
+    Declare Property empty As Boolean
+    Declare Property front As T
+    Declare Function pop() As T
+    Declare Sub push(item As T)
+  Private:
+    a(any) As T
+    count_ As Integer = 0
+    Declare Function resize(size As Integer) As Integer
+End Type
+
+Constructor Queue(T)()
+  Redim a(0 To 0) '' create a default T instance for various purposes
+End Constructor
+
+Destructor Queue(T)()
+  Erase a
+End Destructor
+
+Property Queue(T).capacity As Integer
+  Return UBound(a)
+End Property
+
+Property Queue(T).count As Integer
+  Return count_
+End Property
+
+Property Queue(T).empty As Boolean
+  Return count_ = 0
+End Property
+
+Property Queue(T).front As T
+  If count_ > 0 Then
+    Return a(1)
+  End If
+  Print "Error: Attempted to access 'front' element of an empty queue"
+  Return a(0)  '' return default element
+End Property
+
+Function Queue(T).pop() As T
+  If count_ > 0 Then
+    Dim value As T = a(1)
+    If count_ > 1 Then  '' move remaining elements to fill space vacated
+      For i As Integer = 2 To count_
+        a(i - 1) = a(i)
+      Next
+    End If
+    a(count_) = a(0)  '' zero last element
+    count_ -= 1
+    Return value
+  End If
+  Print "Error: Attempted to remove 'front' element of an empty queue"
+  Return a(0)  '' return default element
+End Function
+
+Sub Queue(T).push(item As T)
+  Dim size As Integer = UBound(a)
+  count_ += 1
+  If count_ >  size Then
+    size = resize(size)
+    Redim Preserve a(0 to size)
+  End If
+  a(count_) = item
+End Sub
+
+Function Queue(T).resize(size As Integer) As Integer
+  If size = 0 Then
+    size = 4
+  ElseIf size <= 32 Then
+    size  = 2 * size
+  Else
+    size += 32
+  End If
+  Return size
+End Function
+#EndMacro