Friday, October 29, 2010

c# "new" keyword - 3 meanings

I'm sure there are excellent online articles, but here's my own learning note.

Java "new" always hits Heap, period. Simple and clean.

C++ has array-new, placement-new, and class-specific-new. C++ "new" almost always hits the heap except
- except placement-new
- except you can customize op-new for your class to hit your allocator.

C# "new" doesn't always mean Heap. The code "new MyStruct" usually hits the stack rather than the heap. See P55[[c#precisely]] for a nice diagram.

C# actually gives 3 unrelated (mildly confusion) meanings to the "new" keyword. One is the Java meaning. The 2nd meaning is "hide base type Member" and can apply to
* virtual methods -- Most confusing
* non-virtual methods
* fields
* nested classes/interfaces
* events??

"Type" can be a base interface.

3rd meaning - select-new creates an instance of an anonymous type [3]. See http://www.dotnetperls.com/select-new.  http://stackoverflow.com/questions/2263242/select-new-keyword-combination is a summary of select-new

[3] java also let's you create an instance of an anonymous type but you need to specify the supertype.

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