Why does the return statement have to be t.x; ?

Guest User

Hi

Given the following code I came across:-

class MyImmutableType
{
public readonly double x;
public MyImmutableType(double _x) { x = _x; }
public MyImmutableType Square() { return new MyImmutableType(x*x); }
}

static double SomeMethod(MyImmutableType t)
{
t = t.Square();
return t.x;
}

Why does the return statement have to be t.x;
rather than just t, as t holds the return value of Square?

I appreciate that the return type of SomeMethod is double and x is of type double so it could be due to a type conversion\cast error.

Regards
Steven

3 Replies

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Vulpes14y ago
Accepted answer
In general, a return statement must be followed by an expression which has the same type, or is implicitly convertible to the same type, as the return type of the method itself.

The return type of SomeMethod is double and the type of t.x is double, whereas the type of t is MyImmutableType. So the former matches but the latter does not.
Akkiraju Ivaturi14y ago
Add one more public property int in your class MyImmutableType.

Let us call it myId.

Now when you create an instance of MyImmutableType in the Main() method,

assign value to the property myID =178.
Debug the code by pressing F10 button. Before moving to the code t=t.square() check what is the value myID of "t". It shows 178. Now after executing t=t.square(), you check the value of myID and it shows 0.

This is because the square method of t is returning a new type and when you say executing square method, you are actually finding the square of x in the type t and not t. x is the double type which should be returned by your someMethod not myImmutableType. But why you are assigning t.square() to another myImmutable type is the square method return type is not a double, but the myImmutable type. What the square method returns is it squares the x in type t and returns type t.

So, you cannot return t as the value, but it should t.x.
Guest User14y ago
I cant even get this code to work anyhow as the return statement, return new MyImmutableType(x*x); errors with "x does not exist in the current context" so I need to pass in an integer value ie 2 for it to work...