Early returns vs nested positive if statements

Question

Here is some hypothetical code sample:

if (e.KeyCode == Keys.Enter)
{
    if (this.CurrentElement == null) {
        return false;}

    if (this.CurrentElement == this.MasterElement) {
        return false;}

    if (!Validator.Exist (this.CurrentElement)) {
        return false;}

    if (!Identifier.IsPictureElement (this.CurrentElement)) {
        return false;}

    this.FlattenObjects(this.CurrentElement);
}

VS

if (e.KeyCode == Keys.Enter)
{
    if (this.CurrentElement != null) {

        if (this.CurrentElement != this.MasterElement) {

            if (Validator.Exist (this.CurrentElement)) {

                if (Identifier.IsPictureElement (this.CurrentElement)) {

                    this.FlattenObjects(this.CurrentElement);}}}}}}

}

Which one do you think is better in terms of readability, maintenance, etc?

Also the 2nd example can be formatted differently via the different use of parenthesis.

Answer 1

Early returns are much more readable.

Whenever you get more than four or five levels of nesting inside a method, it's time to refactor that method.

A single if with an || clause can sometimes be more readable:

if (this.CurrentElement == null
 || this.CurrentElement == this.MasterElement
 || !Validator.Exist(this.CurrentElement)
 || !Identifier.IsPictureElement(this.CurrentElement))
    return false;

Answer 2

The first example is better in every way. It's simpler, and easier to read. Some people say that every function should have a single return point; this example shows clearly why those people are wrong.

PS Personally I would remove all those superfluous curly brackets:

if (this.CurrentElement == null) return false;

etc. This makes it even simpler, and even easier to read.