What's the difference between a comma separated conditional and one that uses a double ampersand [duplicate]

Question

I've recently come across this type of scenario using if/let and understand what it does thanks to this post. To my understanding, both conditions need to be met before the proceeding block is executed. I now have come to a point where I've seen it in a regular conditional statement:

if existingTextHasDecimalSeparator != nil, replacementTextHasDecimalSeparator != nil {
    return false
} else {
    return true
}

What's the difference between doing the above and simply using && as seen below?:

if existingTextHasDecimalSeparator != nil && replacementTextHasDecimalSeparator != nil {
    return false
} else {
    return true
}

Answer 1

There does not appear to be a difference between using && for grouping conditionals and using commas. I too have so far only seen it used with optional binding, but apparently it also works for regular conditionals, as the following snippet works fine.

let bool1 = true;
let bool2 = true;

if bool1 , bool2 {
    print("true");
} else {
    print("false")
}

Answer 2

The comma is used when optional binding with boolean conditions, for example if let a = a, a.isValid() whereas && is a typical AND operator