I am working on retrofitting an application written in VB.NET. It is a simple program that uses 0.5GB (!) of RAM, because of a large amount (30+) of globally defined arrays, like:
Public Temp(1000000) As Double
Public ThisIsAnotherVariable(5000, 10) As String
Public ThisIsAVeryLargeArray(64, 50000) As Double
Most of the time, these large "buffers" are barely used, so I would like to convert them to use something from Collections.Generic. Is there any semi-transparent way to convert these? Or a bit of trickery to get the CLR to only allocate the used segments?
If these are "sparse" arrays, i.e., if almost all array entries are entries, the simplest solution might be to replace them with dictionaries:
Public Temp(1000000) As Double ' Old
Public Temp As New Dictionary(Of Int32, Double)() ' New
Assignment would be source-code compatible:
Temp(10) = 2.0 ' Works for arrays and dictionaries
Reading would be source-code compatible, if the value is present:
Dim x = Temp(3) ' Works for arrays and dictionary, if Temp(3) has been assigned
However, accessing values which have not been assigned will yield a KeyNotFoundException. If you need that, you'd have to use a "default value dictionary" instead of a regular dictionary. Unfortunately, no such dictionary is built-in in the BCL, but there are others who have already looked at that problem and shared their implementation. If you want to use a plain .NET dictionary, you will need to replace every read access with a method call.