Would simple class instantiation ever fail in C#?

Question

I saw some code written by another developer that looks something like this:

var stringBuilder = new StringBuilder();

if(stringBuilder == null)
{
    // Log memory allocation error
    // ...
    return;
}

(It is ALL over the place in the code )

Question 1: Would that error logging code even get called? If there was no memory, wouldn't an System.OutOfMemoryException be thrown on that first line?

Question 2: Can a call to a constructor ever return null?

Answer 1

You're correct, and that code is wrong. It will throw OutOfMemoryException on a failure. This is clear in the documentation:

"If the new operator fails to allocate memory, it throws the exception OutOfMemoryException."

Constructors don't return anything, let alone null. They manipulate an object that's already been allocated.

Answer 2

My assumption is that the coder used to work in C++, and doesn't know how things work in C#.

Answer 3

1. No. An OutOfMemoryException will be thrown if there isn't enough memory available to allocate an object.
2. No

Answer 4

Now, this code is a different story:

StringBuilder stringBuilder = null;

try { stringBuilder = new StringBuilder(); } catch(Exception) {}

if(stringBuilder == null)
{
    // Log memory allocation error
    // ...
    return;
}

In that case, string builder could (conceivably) be null.

Answer 5

Here is a better version of the code. You would have much bigger problems if there is not enough memory to allocate a reference though.

StringBuilder stringBuilder = null;

try {
   stringBuilder = new StringBuilder();
}
catch(OutOfMemoryException) {
   // log memory error
}