Power-Ups and Singletons - Pro Unity Game Development with C# - page 122

Before reading the following comments, execute this code in Unity and look inside the Console
window to see what happens. The result is shown in Figure 4-7 .
Figure 4-7. Using coroutines. Notice that the string “Counter Finished”, which occurs inside Start on a line after the function
Counter is called, is actually printed before the counter function completes!
 Lines 07 and 18. Both of these lines declare a coroutine. Notice that many
Unity events, like Start , can be declared as a coroutine. They need not always
return void . Coroutines are always declared with an IEnumerator return type,
and they always feature a yield statement somewhere in their body. Technically,
a function that returns a type of IEnumerator and has a yield statement in its
body is a coroutine. So in Listing 4-6, both Start and Counter are coroutines.
 Line 10. In this class, the Start coroutine is invoked automatically by Unity, just
as it invokes the normal Start event, but line 10 invokes a coroutine manually.
Notice that a coroutine cannot be called like a regular function. Instead, the
function StartCoroutine must be used to initiate the specified coroutine. If
you've actually tested and run this code, you'll see from the output in the
Console window, and from Figure 4-7 , that the Counter coroutine is executed,
but Start does not wait for it to finish before resuming execution on the next line
at line 13. Line 13 is executed, and “Counter Finished” is printed to the console
before the Counter coroutine is completed entirely. This demonstrates the
asynchronous behavior of coroutines.