How Does Knowing Ref and Val types Help

Question

I have been reading up on Reference and value types. I get the idea. But how does this help me while coding? I don't have any good examples to understand those times where knowing this stuff helps.

Answer 1

It means you can understand what your code is going to do.

It's kinda hard to write code when you can't predict what the effects of any given statement will be, due to not knowing the type system semantics.

For example, suppose you don't know how reference types work, and someone presented you with this code:

StringBuilder builder = new StringBuilder();
StringBuilder other = builder;
builder.Append("Foo");
other.Append("Bar");
Console.WriteLine(builder);

We know that that will print "FooBar" because StringBuilder is a reference type - the second line is only copying a reference, not creating another object. But if you didn't understand how reference types behave, you might have expected it just to print "Foo".

Answer 2

Value types and reference types differ in how they work, how they are optimised, where they are stored etc. Although you can probably get away with writing applications without any real knowledge of how they differ, it is so much more beneficial to understand and appreciate why you use certain types for certain things.

For instance:

• Why can't I assign a null to my int?
• Why when I pass in an integer into a function does it not update my local variable?
• Where are variables stored in memory?

It's a fundamental part of the design of the runtime. Let's not forget that it comes straight out of the Interviewer's question handbook!

Answer 3

For example:

void ChangeDate(DateTime dt)
{
   dt.Year = 2011;
}

DateTime dt = new DateTime(2010,1,1);
ChangeDate(dt);
Console.WriteLine(dt);

Since DateTime is a struct (value type), it is passed by value (if not the in,out or ref specifiers are present). The console output here still prints 2010.

What is going on? Since DateTime is passed by value, a copy of that object is passed into the method. If the method modifies the object, only the copy is modified.

So what is new good for? reference objects are created on the heap and must be allocated first. This is different for value types. The new operator for value types just copies an initialized object over your old object.

Answer 4

Suppose you see this code:

    static void changeVal (Foo i){
        i.Int = 5;
    }       

    public static void RunSnippet()
    {
        Foo foo = new Foo(){Int = 0};

        changeVal(foo);
        Console.WriteLine(foo.Int);             
    }

Can you predict output? No, because if Foo is class then you will get 5 and if it is struct you'll get 0.