Question

So I have this;

var emailA = ConstructEmailA();
SnedEmailA(emailA.Append("</body>").ToString());

var emailB = ConstructEmailB(emailA);
SendEmailB(emailB.ToString());

Which works fine. Essentially, ConstructEmailB takes emailA and adds to it. However, I originally had this:

var emailA = ConstructEmailA();
var emailB = ConstructEmailB(emailA);
SnedEmailA(emailA.Append("</body>").ToString());                
SendEmailB(emailB.ToString());

Which did not work as expected. Instead of emailA and emailB being different, emailA contained the same info as emailB. How come?

Here is my ConstructEmailB method:

private StringBuilder ConstructEmailB(StringBuilder email)
{
    email.Append("Append stuff");

    return email;
}

Answer 1

Which did not work as expected. Instead of emailA and emailB being different, emailA contained the same info as emailB. How come?

Because emailA is emailB. They are both references to the same StringBuilder object, the only difference being when you call SendEmail. In the first case you

1. construct emailA.
2. Append to emailA.
3. Capture the value at that point in time and send it to SendEmailA.
4. “Construct emailB, which is really just appending to emailA and then send that.

In case 2 you have:

1. Construct emailA and emailB. They are identical because they are both references to the same StringBuilder.
2. Append ' to emailA (and thus, also to emailB) and send it.
3. Send emailB.