sema: a theme that focuses on what’s important

When we write code, we do it in colour.

fn under_threshold(self) -> bool {
    if let Some(reset_threshold) = self.config.reset_threshold() {
        self.terminal.portion_covered() < reset_threshold
    } else {
        true
    }
}

You already do the kind of highlighting shown here in your head.

To read code in the first place, you make sense of the syntax as you go.

Just by looking you can tell that if is a keyword, that do_thing() is a function call and that 100 is a number – no highlighting required.

Let’s spend the ‘colour budget’ on important things instead of the easy stuff we do automatically anyway.

We can only stand so many different bright colours in our code before it becomes an overwhelming rainbow. Let’s give colour to those elements of code that are particularly confusing and lead to bugs easily.

This is a debatable topic, but I would argue that there are a few clear contenders:

• control flow – easy to make mistakes with
• interfaces/traits – ‘where did this method come from?’
• magic numbers and strings – their purpose is often unclear and so deserve more attention
• mutation – ‘why is this variable’s value not what I expected it to be?’

Here’s some code that has all four – try to spot them.

fn do_thing() {
    var api = JsonApi.connect();

    loop {
        if api.read_value() == 294 {
            print("Success!");
            "127.0.0.1:8080".make_current_socket(api);
        }

        print(api.connected_socket);
    }
}

What would code look like if we emphasised the difficult parts?

fn do_thing() {
      var api = JsonApi.connect();

      loop {
        if api.read_value() == 294 {
            print("Success!");
            "127.0.0.1:8080".make_current_socket(api);
        }

        print(api.connected_socket);
    }
}

How did the make_current_socket method appear on the string literal? It came from an interface, which is now obvious due to the bright colour. The magic numbers and strings stand out more, as does control flow.

make_current_socket modifies its arguments, which would’ve surprised us with the old theme when we printed the API’s connected socket and found it had changed. With this theme, the underline lets us know beforehand. api’s underline shows that it can be mutated, an additional reminder.

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