The Ultimate Breakdown of Kotlin Coroutines. Part 5. Suspend Functions.
Previous parts covered suspend lambdas and the machinery, which makes coroutines tick - suspend and resume. Also, I covered continuations, state-machines and interception. There is only one part remaining - suspend functions. I will omit coroutines inlining, which despite having complicated implementation, has an easy mental model - inlining does not affect behavior of coroutines. All the inlining is done prior to state-machine transformation. Finally, I will omit optimizations for the same reason - they do not change the behavior. Suspend Functions As explained in the continuation-passing style section, every suspending function's signature is changed: the compiler adds a continuation parameter and changes the return type to Any? . The tricky part becomes when we try to make it suspendable, in other words, when we build a state machine and generate a continuation. Unlike suspend lambdas, we cannot reuse an existing class for the continuation, since the suspend function can be s...