Question

In PS4 what is the difference between the build_coder and the build_encoder functions?

Answer 1

build_coder can shift in both the positive and negative direction, and is meant to be used as a helper function for build_encoder and build_decoder. build_encoder only shifts in the positive direction, and is only meant to encode messages (as opposed to decoding them).

Answer 2

The implementation of build_coder should be short - it only calls the build_decoder or build_encoder as needed. This is an example of using abstraction. Someone using your code doesn't have to worry about what they should use (build_encoder or build_decoder) if they just want to build a coder.