Static Typing, IDEs, Automated Testing: An Eternal Golden Braid

I've been a programmer by trade ever since I graduated from University. This is a fairly long time, as these things are measured. I still consider myself on a learning curve, but that's a separate conversation.

My career, such as it is, mostly sidestepped the whole static versus dynamic typing debate that roiled in the early 2000's. School, when it veered into software territory, mostly consisted of C and Java, two statically typed languages. My professional life, until fairly recently, has been mostly in Java (with a bit of C++ thrown in for good measure) and hence has almost exclusively revolved around statically typed languages.

For those not in the know, a statically typed language is able to catch certain kinds of errors at compile time that a dynamically typed language cannot. Consider the following example:

StaticTyping.java:

public class StaticTyping {
    public static void main(String[] args) {
        int a = 6;
        String b = "3";
        int c = a / b;
        System.out.println("This is c: " + c);
    }
}

This example won't compile, because you can't divide an integer by a String. On the other hand, consider the equivalent example in Python:

dynamic_typing.py:

a = 6
b = "3"
print a / b

This will also fail, but only at runtime. This may not seem like such a big deal, but it becomes a bit more insidious when you modify the example slightly:

dynamic_typing_insidious.py:

def func1():
    a = 6
    b = "3"
    print a / b

def func2():
    a = 6
    b = 3
    print a / b

func2()

This will run fine, despite the obvious error lurking in func1(). The error would only ever come to light when you run func1(). This is what people mean when they claim that static languages are safer.

(Proponents of dynamically typed languages will claim at this point that automated testing helps to offset some of the risk here, and they are not wrong. See later in this article for a brief discussion of this).

One could say, without much exaggeration, that my current employer loves static typing. Even in the context of web applications, where one might expect JavaScript to reign supreme, the preferred solution for a long time was to use GWT whenever possible. Perl, Python, and JavaScript were used, but not to the same extent, and certainly not for anything that could be considered an "application". I taught myself Perl and Python at home to give myself some balance, and I now consider myself a reasonably seasoned Python programmer, but for me dynamic languages still have a bit of a "hobby" feel to them.

Java is, after all, what I used every day for many years. To say that my work languages were all statically typed requires, therefore, some qualification. It is more accurate to say that they were statically typed in the style of Java.

This is an important point because while there have always been other statically typed languages with a much different feel to them, the industry, until fairly recently, has mostly embraced Java and so this is the language that is traditionally brought up in any static versus dynamic typing debate. It is the canonical statically typed language, usually pitted against canonical dynamically typed languages like JavaScript, Python and Ruby.

This muddies the waters somewhat, because it is well-known that Java's relatively primitive typing system can lead to notoriously ceremonial code. When people extol the virtues of a dynamically typed language like Python, they are usually comparing it against a language like Java. A language like Python (or JavaScript) often shines in such a comparison, because it's much less verbose, and a much easier language in which to get something up and running in a relatively short amount of time.

The TypeScript Experiment

There are, of course, many other statically-typed languages than Java, but the only one with which I have any degree of familiarity would be TypeScript. TypeScript is probably best described as EcmaScript 6 (i.e. modern JavaScript) with optional static typing added.

People are often skeptical of TypeScript when they first come across it because a) it was developed and is currently maintained by Microsoft and b) their only basis for comparison (I'm guessing) are other transpiled systems like CoffeeScript and GWT, both of which have their issues. Using CoffeeScript, for example, requires learning an entirely new (dynamically typed) language which consists of almost pure syntactic sugar over EcmaScript 5 - a lot of which is obviated with the introduction of EcmaScript 6. GWT, on the other hand, being Java, comes with its attendant verbosity and ceremony, and makes it difficult to integrate 3rd party JavaScript libraries.

TypeScript is different. TypeScript is a superset of JavaScript; you can write standard EcmaScript 5 code and it will be recognized as valid TypeScript code. You can also write more or less standard EcmaScript 6 code and transpile it to standard EcmaScript 5 code (a la Babel). Perhaps most importantly, however, you can optionally add static typing to your code and the transpiler will enforce it.

This last part is key. The static typing in TypeScript is optional and inferred; unlike Java, it's not an all-or-nothing proposition. You don't have to add a type to every variable to make use of it, and this makes it fundamentally less verbose than Java.

I think that a language like TypeScript drastically changes the calculus of the static versus dynamic debate. When your only alternative to JavaScript is something like Java, many people, understandably, prefer to stick with JavaScript. But when you have something like TypeScript available, where the language is familiar and the typing is unobtrusive, the choice is much harder.

In Defence of IDEs

It's safe to say that I'm a fan of TypeScript. Using it comes with very little downside. In theory, the upside, as with any statically typed language, is that the transpiler would be able to catch certain kinds of bugs up front that, for a dynamically typed language, would only ever be caught at runtime.

Honestly, though? In my experience, the bug-catching aspects of statically typed languages are overblown. To be sure, TypeScript has caught a handful of bugs in my own code, but I wouldn't say that it's caught enough for this to be the sole reason to use it. Although there is very little downside to using TypeScript, it's not zero - you still need to download and set up the compiler, the code you write is no longer directly usable is a browser, and you have to use a new linting tool.

So why use Typescript? For me, there are two main reasons:

1. Type annotations are an excellent form of documentation
2. IDEs suddenly become much more useful

The first is perhaps less controversial than the second. It's useful to know, by looking at the code, if a variable is supposed to be a number or a string, or a collection thereof. It's especially useful in conjunction with libraries like lodash and rxjs, which often transform collections and Observables from one form to another in ways that are not entirely obvious at first glance. I'll often find myself adding an explicit type declaration to an intermediate variable even when type inference would normally figure it out, just for the clarity it provides. Of course, you can do the same thing with a comment, but the type declaration has the added advantage of being compiler enforceable while remaining just as readable.

I say that the second point is controversial because I know that there are a large number of dynamic language advocates who take pride in their habit of writing code without an Integrated Development Environment (IDE). Java programmers almost never do that since writing Java without an IDE is torture. Often this leads people to conclude that an IDE is merely a crutch for covering up flaws in your language of choice; there would be no need for an IDE, so the argument goes, if Java were less verbose.

While I see the point, I think it's a bit simplistic. It's true that part of the reason one uses an IDE in conjunction with Java is to facilitate the cranking out of code constructs that are tedious to write by hand - constructs which are unnecessary in other languages. But it is also true that an IDE is useful for much more:

• automatic import management
• jump to function definition
• auto completion
• refactoring tools, like method and variable renaming
• on-the-fly detection of compile errors and warnings.

You can, of course, learn to live without any of this, but why would you want to? All of the above is staggeringly useful, especially as the size of your project grows.

More to the point, all of the above is greatly facilitated by the use of a statically typed language, because it's possible to deduce more about your code up front than is possible with a dynamically typed one.

On the Use of Test Suites

While it is, of course, silly and wrong to suggest that a strong focus on automated testing and the use of a statically typed language are mutually exclusive, the practice does tend to be associated more with dynamically typed languages. The received wisdom is that the test coverage makes up for the lack of compile time error checking; in a sense, your test suite fulfills the role of a statically typed compiler, catching basic issues in advance. When a dynamic language advocate is confronted with the assertion that a static language catches certain kinds bugs that a dynamic language cannot, they will often just wave their hand, shout "unit tests!", and move on.

Alright, I'm exaggerating. But only slightly.

I understand the sentiment, but I feel it rests on an incorrect assumption. Many people think that the main purpose of an automated testing suite is to catch bugs. While this is certainly a useful side effect, I find that a test suite's main use lies in its role as documentation.

A test suite, at its best, documents developer expectations, and when your code base gets to be a certain size, this is invaluable. Debugging in unfamiliar code is often a two-pronged challenge because not only are you trying to find a defect, you're often, at the same time, trying to figure out what the right answer is supposed to look like. You are, in other words, trying to figure out what the developer meant to do. An automated test suite, when written the right way, can help immensely with this, wherever you fall on the dynamic/static divide.

Conclusions

Ultimately, I guess what I'm trying to say is the following:

• Static typing is a win, as long as it's the right kind of static typing. Otherwise all bets are off.

• Automated test suites are a win, whether you use a static language or dynamic language, as long as they are written primarily for the purpose of documenting developer expectations.

• IDEs are a win, just because they're so darn useful. And static typing makes IDEs work better.