POMO Exercise

#
# POMO - Principal of Mutual Oblivion
#

Two modules at the same level of abstraction should not know each other. ("mutual oblivion" - not knowing each other)

It is the independece of parts - no functional units knows another one. They are all completely independent of each other. - Ralf Westphal 

Example - muscle movement in human bodies:
A nerve cell does not know anything about a muscle cell and a muscle cell does not know anything about a nerve cell. All they do is follow a simple contract: Acetylcholine (ACh) - one produces ACh as output, the other consumes ACh as input.
The cells forming your body do not know each other. Each cell is independent and does not have a clue what is going on on a higher level.
It is only when integrating these parts, that we get a "controlled" movement. So "control" is a higher level concept of the whole, not of its parts.

Nature follows this simple recipe to produce complex systems that work.

The Unix philosophy follows a similar approach, it emphasizes simple, short, clear, modular, and extensible code and favors composability:
* Write programs that do one thing and do it well.
* Write programs to work together.


#
# Bad Example
#

* CreateJob() knows technical details of ApplyJob (how to build a http request)
* the technical concern of the http request is scattered around in two functions

public void Deploy(string computerName)
{
    var job = CreateJob(string computerName);
    var success = ApplyJob(job);
}

public Job CreateJob(string computerName)
{
    return new Job
    {
        HttpVerb = "POST",
        HttpPath = "/Deployment",
        HttpBody = GenerateRequestBody(computerName), // 'string'
    };
}

function bool ApplyJob(Job job)
{
    if (job.HttpVerb == "POST") {
        var url = _serverUrl + job.HttpPath;
        var body = job.HttpBody;
    }
    if (job.HttpVerb == "GET") {
    }
}


#
# Good Example
#

* CreateJob() is only concerned about building the Job object and has no clue what is going to happen with this object

public void Deploy(string computerName)
{
    var job = CreateJob(string computerName);
    var success = ApplyJob(job);
}

public Job CreateJob(string computerName)
{
    return new Job
    {
        Type = TYPE_DEPLOYMENT;
        Data = GenerateDeployment(computerName), // 'Deployment' object
    };
}

function bool ApplyJob(JobAction job)
{
    if (job.Type == TYPE_DEPLOYMENT) {
        var url = _serverUrl + "/Deployment";
        var httpVerb = "POST";
        var body = JsonConvert.SerializeObject(job.Data);
        ...
    }
    if (job.Type == TYPE_REMOVE) {
    }
}


#
# Exception to the rule
#

* CreateJob() has basic knowledge that ApplyJob() will generate a request (json body)

public void Deploy(string computerName)
{
    var job = CreateJob(string computerName);
    var success = ApplyJob(job);
}

public Job CreateJob(string computerName)
{
    return new Job
    {
        Type = TYPE_DEPLOYMENT;
        Data = GenerateDeployment(computerName), // 'string'
    };
}

function bool ApplyJob(JobAction job)
{
    if (job.Type == TYPE_DEPLOYMENT) {
        var url = _serverUrl + "/Deployment";
        var httpVerb = "POST";
        var body = job.Data;
        ...
    }
    if (job.Type == TYPE_REMOVE) {
    }
}