Question

I stumbled across this while starting to learn about vars here:

http://msdn.microsoft.com/en-us/library/bb384061.aspx

However, I have no idea how that is a legal expression (it is). I thought you couldn’t assign to something using an a = (b=c) because (b=c) does not produce a value to assign?

Thanks for any clarification on the matter.

Answer 1

It is legal. From the = operator C# reference page:

The assignment operator (=) stores the value of its right-hand operand in the storage location, property, or indexer denoted by its left-hand operand and returns the value as its result.

(emphasis mine)

The code in the example is contrived (and pointless), but it can be used in other cases to do useful things in a more concise way. For example:

BinaryTree tree;
TreeNode node;
if((node = tree.FindNodeForKey(10)) != null)
{
    // do useful things with returned node
}