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Is there any difference in runtime performance between the following variable initializations?
var x = null as object;
var x = (object) null;
object x = null;
305
You should initialize your variables at the top of the class or withing a method if it is a method-local variable. You can initialize to null if you expect to have a setter method called to initialize a reference from another class.
You can make it like this. string y = null; var x = y; This will work because now x can know its type at compile time that is string in this case.
var can only be used when a local variable is declared and initialized in the same statement; the variable cannot be initialized to null, or to a method group or an anonymous function.
In C#, you can assign the null value to any reference variable. The null value simply means that the variable does not refer to an object in memory.
I believe no, since there is no difference in compiled IL.
var x = null as object;
var x1 = (object)null;
object x2 = null;
gets compiled to
IL_0001: ldnull
IL_0002: stloc.0 // x
IL_0003: ldnull
IL_0004: stloc.1 // x1
IL_0005: ldnull
IL_0006: stloc.2 // x2
You can see all the locals are initialized to null using ldnull opcode only, so there is no difference.
183
First of all: No, I believe these three calls are essentially equivalent.
Secondly: Even if there was any difference between them, it would surely be so minuscule that it would be completely irrelevant in an application.
This is such a tiny piece of any program, that focusing on optimization here and in similar situations, will often be a waste of time, and might in some cases make your code more complicated for no good reason.
There is a longer interesting discussion about this on the programmers.stackexchange site.
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