iterating through members of bitfields

[Nestor via Digitalmars-d-learn]

On Friday, 20 January 2017 at 08:13:08 UTC, drug wrote:
> Something like that https://goo.gl/C4nOqw
> Because you generate code iterating over AliasSeq you can do 
> almost everything you need - for example generate 
> setters/getters.

Interesting site, I wouldn't implemente something like this in a 
public server but sure it's useful.

Regarding the example, looks interesting though it raises s a few 
doubts (forgive me if they sound silly):

What's UAP?

Where does one define the size for a field using AliasSeq, and in 
this example, why does it take 1 bit if the size is not declared 
anywhere? (also, why does it compile when the last field 
terminates with a comma?)

alias Fields = AliasSeq!(
	ushort,     "field0",
	ubyte,      "field1",
	uint,       "field2",
	ubyte,      "field3",
	bool,       "field4",
	bool,       "field5",
	bool,       "field6",
	ubyte,      "field7",
);

Why does the switch apply to the remainder of the modulo 
operation, does Fields contains indexes to types and names as if 
it was an array?