Re: Inside the switch statement

[BCS]

Hello Sam,

To save time ,just get to my point:I do not understand why such code
below inside the switch ... case statement is allowed ,what is the
point of do ... while...:

This is a classic C thing. The short explanation is that a switch is a conditional, 
many way goto and the labels can be *anywhere* in the body (except inside 
another switch). For the more in depth version Google "duff's device".


This example uses a mixin to implement a generic Duff's device for an
arbitrary statement (in this case, the arbitrary statement is in
bold).

BTW: where is this from?

A nested function is generated as well as a delegate literal,
these can be inlined by the compiler:
template duffs_device(alias id1, alias id2, alias s)
{
void duff_loop()
{
if (id1 < id2)
{
typeof(id1) n = (id2 - id1 + 7) / 8;
switch ((id2 - id1) % 8)
{
case 0:        do {  s();
case 7:              s();
case 6:              s();
case 5:              s();
case 4:              s();
case 3:              s();
case 2:              s();
case 1:              s();
} while (--n > 0);
}
}
}
}
void foo() { writefln("foo"); }

void test()
{
int i = 1;
int j = 11;
mixin duffs_device!(i, j, delegate { foo(); } );
duff_loop();    // executes foo() 10 times
}