What is the difference between Switch-Case and If-Else in PHP?

Interesting question because in a compiled languaged (or JIT'ed language even) there is a nice performance gain when using switch statements because the compiler can build jump tables and will run in constant time. Even switching on a string can be optimized as the string can be hashed. However, from what I've read, it appears php makes no such optimization (I'm assuming because it's interpreted and runs line by line).

Great .Net article about switch optimization: If vs. Switch Speed

Regarding php being interpreted, the PHP docs says: http://php.net/manual/en/control-structures.switch.php

It is important to understand how the switch statement is executed in order to avoid mistakes. The switch statement executes line by line (actually, statement by statement). In the beginning, no code is executed. Only when a case statement is found with a value that matches the value of the switch expression does PHP begin to execute the statements. PHP continues to execute the statements until the end of the switch block, or the first time it sees a break statement. If you don't write a break statement at the end of a case's statement list, PHP will go on executing the statements of the following case.

I also found several references all suggesting that if / else statements in php may actually be faster than switch statements (weird). This probably is not true if you compile php (something I've never done, but apparently it's possible).

http://www.fluffycat.com/PHP-Design-Patterns/PHP-Performance-Tuning-if-VS-switch/

This article in particular, http://php100.wordpress.com/2009/06/26/php-performance-google/, is interesting as the author compares internal php code of if vs switch and they are nearly identical.

Anyways, I would say that any performance gain will be insignificant one way or the other, so it's more of a user preference. If statements are more flexible and you can more easily capture ranges of values (especially large ranges) as well as do more complex comparisons whereas switch statements line up to exactly one value.

When you use self to refer to a class member, you're referring to the class within which you use the keyword. In this case, your Foo class defines a protected static property called $bar. When you use self in the Foo class to refer to the property, you're referencing the same class.

Therefore if you tried to use self::$bar elsewhere in your Foo class but you had a Bar class with a different value for the property, it would use Foo::$bar instead of Bar::$bar, which may not be what you intend:

class Foo
{
    protected static $bar = 1234;
}

class Bar extends Foo
{
    protected static $bar = 4321;
}

When you call a method via static, you're invoking a feature called late static bindings (introduced in PHP 5.3).

In the above scenario, using self will result in Foo::$bar(1234). And using static will result in Bar::$bar (4321) because with static, the interpreter takes takes into account the redeclaration within the Bar class during runtime.

You typically use late static bindings for methods or even the class itself, rather than properties, as you don't often redeclare properties in subclasses; an example of using the static keyword for invoking a late-bound constructor can be found in this related question: New self vs. new static

However, that doesn't preclude using static with properties as well.

You have the right idea.Internally these devices are VLAN switches with exposed ports a member of a single vlan + a single port computer to do routing between vlans and configured to look like a dumb switch and wan port

If you can run it, DD-WRT for example - exposes the internal workings somewhat - typically all 5 ports - the WAN port included - are VLAN switch ports- with another invisible VLAN trunk port on the motherboard.

It is thus (software permitting - and most software does not) possible to combine ports so they are all on the same VLAN and appear as a dumb switch, or you can break them out on to separate vlans and have multiple "WAN" ports, or multiple lan subnets.

It is certainly possible to connect the WAN port to a separate subnet, say to an another switch or to an another router - really, that, and having a route table is the core requirement of a router.