Should we avoid string?

No overview of memory issues in C# and Unity would be complete without mentioning strings. From a memory standpoint, strings are strange because they are both heap-allocated and immutable. When you concatenate two strings (be they variables or string-constants) as in:

void Update()
{
    string string1 = "Two";
    string string2 = "One" + string1 + "Three";
}

... the runtime has to allocate at least one new string object that contains the result. In String.Concat() this is done efficiently via an external method called FastAllocateString(), but there is no way of getting around the heap allocation (40 Bytes on my system in the example above). If you need to modify or concatenate strings at runtime, use System.Text.StringBuilder.