.NET Placement New

Question

Is there a placement new in .NET (like C++)?

In other words if I allocate some memory in VB.NET

Dim Foo(64) as Byte

I want to instance BarClass in the Foo memory (something like...)

Dim Bar as New BarClass(Foo)

However, I don't see any syntax to do this.

Instead I have to do something like:

Dim Foo(1) as BarClass
Foo(0) = new BarClass(x, y, z)
Foo(1) = new BarClass(x, y, z)

Answer 1

No, there is no equivelent in .NET.

In addition, the GC is free to move your object around in memory whenever it wants (provided it hasn't been pinned to a location). This type of behavior is typically something that's avoided in most .NET code.

You can work around this by using native code and interop.

Answer 2

Take a look at LayoutKind. Setting to explicit will give you c++ union like behaviour.

Answer 3

The reason you use placements in C++ is because when you ask for 64 bytes of memory, the operating system really gives you 64 bytes of memory. So if you need to create a bunch of objects at once it's more efficient to allocate a larger block of memory up front and create each new object with a segment of that block.

In managed languages like C#, this is already done for you. When you ask for 64 bytes of memory the framework allocates an entire block and gives you 64 bytes out of that block (or another previously allocated block).

Answer 4

Why don't you just do an array initialization? Dim values() As BarClass = {new BarClass(x,y,z), new BarClass(x,y,z)}