Today was day one of the Summer 2 batch, meaning we got thirty new people! This also means we had our first day without the Spring 2 batch, who I’ll definitely miss. But several of them showed up for a games night so it’s almost like they’re still here.

It was interesting to see the intro talks again from six weeks in. A bit of deja vu, and a good point to really stop and reflect. The advice from the faculty was different the second time, even though the words were the same. Our batch also gave advice or other thoughts to the new Recursers—Sophie jotted it all down.

EcmaScript 15

The morning was taken up with welcoming the new batch, so it was a while until I got back to programming. I decided to start learning JavaScript / ES15 with [es6katas][]. There’s a lot of interdependence between the exercises! I started off with the Arrays collection, but had to take a detour into destructuring. I should have also taken a detour into iterables, as I wasn’t clear on what an ES15 iterator was, and it was needed.

So far ES15 looks pretty nice! I’m almost glad I put off learning JS for so long. Destructuring is especially good. It’s similar to Python, but a bit more versatile. The big features I noticed:

  • fields of objects can be destructured like so:

    let dessert = { name: "eton mess", tasty: true };
let {name} = dessert;
console.log(name);  // => "eton mess"

    It was a bit mysterious to me at first, but this also applies to fields on builtin types, eg, length on String:

    let a = "hi";
let {length} = a;
console.log(length);  // => 2

    (I just realised I should check if this works for properties with getters or not.)

  • you can choose a name to bind to different from the attribute name with a colon, eg,

    let a = "hi";
let {length:l} = a;
console.log(l);  // => 2

  • you can supply defaults when destructuring which is cool! It works when you use the default name for a binding, as well as when you change it, eg,

    let dessert = { name: "eton mess", tasty: true };
let {dairyFree=false} = dessert;  // be safe and assume desserts contain dairy
console.log(dairyFree);  // => false

  • all of this comes together most excellently in using destructuring on a function argument, eg,

    let dessert = { name: "eton mess", tasty: true };
let eat = {name:n, tasty, dairyFree:df=false} => {
    if (!df || !tasty) { console.log("no thanks!"); return; }

    console.log(`mmm yes, I'll eat some ${n}!`);
}

eat(dessert);  // => "no thanks!"

    The default arguments let you have default values in a nice succinct way, and the binding renaming lets you have nice descriptive names in the interface but abbreviate in the implementation.

Planning the second half of RC

Towards the end of the day, I had a worry session with Tom, one of the facilitators. The short of it is I’m worried I’m not going to complete as many things as I want to. I’ve been getting a fair amount of stuff done, but aside from lsaddr I haven’t got much to show for it. While at RC I want to get more comfortable completing things.

Part of this is being afraid of spending too much time on a project that ends up being too big for RC. Of course, at the other end of this, I’m also afraid of spending too much of my time flitting between things. We ended up at the idea of spending a solid day on each of 2-3 projects I have in mind to see where I can get them.

So, my plan for tomorrow is to take what I’ve learned about mmap and start putting it into a Cap’n Proto message builder that writes directly to a memory mapped file. Wish me luck!