# Comment Driven Development

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As most software methodologies grow from some developer’s organizational habit. If the habit helped enough to impact anything significantly, it turns into a method for others to emulate.

Comment driven development is an extremely simple process for breaking apart complex problems into modular (hopefully pure) functions.

Begin with the function in question:

public List<Entity> getFilteredEntities(RailRequest request,
UserGroup group) {
}


public List<Entity> getFilteredEntities(RailRequest request,
UserGroup group) {
// validate request using Railroad Auth
// get user list based on group
// add users to rail request
// filter out entities that have 0 accruals
}


I’ve seen this type of function actually fleshed out in a single function. That is a mistake. Functions should do one clear thing wherever possible. Most devs will just tackle the problem and get it done in one massive tangle, but thinking it through this way simplifies and de-clutters–even if it does seem over-optimistic.

Add a code block under each comment or a function call if it will be more than 10 lines.

public List<Entity> getFilteredEntities(RailRequest request,
UserGroup group) {
// validate request using Railroad Auth
if(!isValidRailRequest(request)){
log.warn("Invalid request");
return Lists.newArrayList();
}
// get user list based on group
List<Integer> users = database.getUsersByGroup(group);
// filter out entities that have 0 accruals
// add users to rail request
return request.getEntities().stream()
.filter(x -> !x.getAccruals().equals(0))