Benefits using StringBuilder rather than String during concatenation or String Building

Question

This is the string reversal method in C# that I was investigating:

string s = "This is the way it is.";
string result = string.Empty;   

for(int i = s.Length-1; i <= 0; i--)
{   
    result = result + s[i];  
}    
return result; 

Assuming that the strings can get very very long. Why is it beneficial to use Stringbuilder in this case over concatenating to result using s[i] as shown above?

Is it because both result and s[i] are immutable strings and therefore an object will get created each time both of them are looked up? Causing a lot of objects to be created and the need to garbage collect all those objects?

Thanks for your time in advance.

Answer 1

NO. Not both of them. Both of strings in this case are immutable. However, look in the for loop, a new result String object is created but not s string object as it is not being updated, we are just accessing it. immediately after the assignment, we have the previous result object illegible for garbage collection as it is loosing reference but not s string object. in the next iterateion, the current new result String object will be garbge collected and so on. had you used string builder, you would have different situation.

 result = result + s[i];

Unlike strings, stringbuilder is mutable. so if your result variable was type of Stringbuilder, new result object would not be created rather the existing one will be updated according to the assignment.