Question

I have a statement where a string is assigned in the following manner:

for (int i = 0; i < x; i++) 
{
    Foo.MyStringProperty = "Bar_" + i.ToString();
    /* ... */
}

Are there any performance differences between i.ToString() or just plain i, as both are just converted to the (culture invariant?) string equivalent?

I am well aware of the existence of String.Concat(), String.Format, StringBuilder, etc., but for the sake of this case, lets assume I may only use + concatenation.

Thanks in advance.

Answer 1

+ concatenation uses String.Concat anyway – String itself doesn’t expose a + operator.

So for example:

int i = 10;
string x = "hello" + i;

is compiled into:

int i = 10;
object o1 = "hello";
object o2 = i; // Note boxing
string x = string.Concat(o1, o2);

Whereas calling ToString directly will avoid boxing and call the Concat(string, string) overload. Therefore the version with the ToString call will be slightly more efficient – but I highly doubt that it’ll be significant, and I’d strongly urge you to go with whichever version you feel is more readable.