C# Assigning mutiple references in one line in if statement

Question

I've seen code where the developer assigns properties or local variables from an if statement after performing some method call.

Example:

    void SomeMethod() 
    {
       MyObject myObject;

       if ((myObject = DoSomething()) != null)
       {
          //Do some business logic
       }
    }

I think it gets very messy when a lot of these assignments are happening, or there is more going on in the if-statement, such as accessing an array.

I personally prefer something like this:

    void SomeMethod() 
    {
       MyObject myObject = DoSomething();

       if (myObject != null)
       {
          //Do some business logic
       }
    }

Is there any benefit of the first piece of code over the second example? Any miniscule efficiency gains or anything? I want to know if I'm missing something.

A large piece of the code set is becoming nested with this style of code which I believe is less readable.

Answer 1

There is no performance implications to this change - it is a matter of personal preference. This works because an assignment is a value-producing expression, which can be used in comparison or other expressions. The idea is to "fold" the assignment into the header of a conditional, essentially saving a line of code.

Although this makes no difference with a single if (the number of lines does not change) it does make a difference for longer chains of conditionals. It is also useful in loops, for example

int ch;
while ((ch = reader.Read()) != -1) {
    // Do something with ch
}