Which solution is of more performance ? Instantiating new object within a for loop

[Nadia Monalisa]

hello, I am confused about choosing a solution between two options and I am not sure which one is of more performance, would you please help me !! Solution A ============

myClass A;

for(int i=0; i < aNumber; i++)
{
A = new myClass(i);

......................
}

Solution B =============

for(int i=0; i < aNumber; i++)
{
myClass A = new myClass(i);

......................
}

[Patrick_N3WB1E]

The solution A is looking like my favorite, its reduced. For one thing whats it for that might change my mind :)

[Luc Pattyn]

Hi, your two code snippets will compile to the same IL instructions and run identically. The only difference is in the scope of A; in solution A, A still has a value when the for loop exits (assuming aNumber is greater than zero); whereas in B, A is dead and burried when the loop exits. :)

Luc Pattyn [Forum Guidelines] [My Articles]

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Fixturized forever. :confused:

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modified on Thursday, December 11, 2008 7:46 PM

[Christian Graus]

The second is better, it's more readable by far. It also limits the scope of the object, and if you don't need it outside the loop, that's a good thing.

Christian Graus Driven to the arms of OSX by Vista.

[PIEBALDconsult]

Yeah, what they said, except B always looks like it'll waste cycles.

[Tony Pottier]

If you just need to run some stuff in A, then throw it away, maybe you should consider adding some kind of "reset" method to myClass which will probably be much faster than instantiating a new object again and again. Just run a quick benchmark with

DateTime start = DateTime.Now;
for(int i=0; i < aNumber; i++)
{
myClass A = new myClass(i);

......................
}
DateTime end = DateTime.Now;
MessageBox.Show( ((TimeSpan)(end-start)).TotalMilliseconds );

[PIEBALDconsult]

That depends on how expensive the instantiation is. A few months ago I spent some time working on a technique to keep using one static StringBuilder throughout a library of static methods; clearing it before each use rather than instantiating (and re-extending as necessary). In the case of StringBuilder, my technique wasn't worth the trouble. :( And for quick benchmarks like that I now use a System.Diagnostics.Stopwatch