Chained IF structure

Question

Imagine this case where I have an object that I need to check a property. However, the object can currently have a null value.

How can I check these two conditions in a single "if" condition?

Currently, I have to do something like this:

if (myObject != null)
{
    if (myObject.Id != pId)
    {
        myObject.Id = pId;
        myObject.Order = pOrder;
    }
}

I would like something like this:

if (myObject != null && myObject.Id != pId)

I want to evaluate the second condition only if the first was true.

Answer 1

if (myObject != null && myObject.Id != pId)
{
   myObject.Id = pId;
   myObject.Order = pOrder;
}

&& is a short-circuiting logic test - it only evaluates the right-hand-side if the left-hand-side is true. Contrast to a & b, which always evaluates both sides (and when used with integral types instead of bool, does a bitwise "and").

Answer 2

It should be stressed that the short-circuited evaluation of the && in the if() is absolutely guaranteed by the language standards (C, C++, Java and C#). It's been that way since the first edition of K&R's "C Programming Language".

It's not something that you have to worry "Does my compiler implement this?". If definitely does.

Answer 3

if (myObject != null && myObject.Id != pId)
{
//bla
}

this is safe because operator && is evaluated lazily, meaning that if the LHS is false, the RHS is never evaluated