I've never understood the so called advantages of dynamic typing. To me it looks like a land mine in one's project waiting to blow at run time. And what for? Do developers code so fast that the time spent on typing something like "int i" will provide any real savings? Now vendors are trying to patch those with bolted on top syntax extensions/derived languages that need to be transpiled. What a mess.
Most people fixate on the terseness that it can afford in a language. I suppose I do like that but for me it is not a huge deal.
What I think is more important is the flexibility that it brings to express design patterns that in other languages, like Java for example, can become very cumbersome. I can’t tell you how many times I have been in the bowels of some Java code and found some method that takes a concrete implementation of something that could or should be an interface when I really want to pass in something different. Then you are like “let me extend and fix this class” and then you end up just extending and fixing 1/2 the code base to get done what needs to be done. In a language like Ruby I would just pass in an object that responds to all the needed methods and it would happily work. Ideally you wouldn't get into these type of messes in statically typed languages because people would follow good design principles all the time. But people are fallible and in reality messes are everywhere in statically typed languages.
So I think the approach of adding type enforcement if desired is a nice approach considering there is a large amount of code out there that probably doesn’t benefit much from it.
When you're consuming JSON that has deep nesting, arrays that contain multiple types, etc. Something that may be two lines of code in a dynamic language could be as much as 100 lines in some static typed languages.
Sure, you could write one line of code to read it in as maps and arrays, but at some point you need to validate your input from the outside world to convert it you your domain objects. Using a dymically typed language doesn't magically make that problem go away.
It makes unit testing much easier. That’s the best explanation I’ve found. Rapid prototyping too, but that just means you’re backloading tech debt so that’s at best neutral in pure technical terms. In a startup context backloading tech debt is deeply desired.
Type checking isn’t really related to typing “int.” Many languages infer types. In fact, Hindley Milner type systems should be able to infer all types without explicitly specifying any of them.
Sometimes I do code that fast. When you’re messing around just trying to find out if something is possible you want to write as much code in as short a time as possible, and Python shines for that. Every second wasted typing is a second that could have been spent moving forward.
Of course the problem is that the prototypes are terrible to maintain and eventually need unit tests and typing. But you don’t want to waste time adding those things if you’re not even sure your idea will work. I use strongly typed languages in production and couldn’t imagine using Python for that.
If typing speed is your main limitation, it means either you can improve your productivity dramatically by improving your typing skills, or your language is limiting you so much that you don't have good abstractions to enable you to think at a higher level.
I don't see how typing F# is slower, longer or less convenient than typing Python (spoiler alert, it's not). And you also get things like actual lambdas, pattern matching, currying, real parallelism and more and more.
It's only that people believe there is no need to learn anything beyond Python because it's "easy", which it's not, once you go beyond several hundred lines of code. But the myth somehow continues to persist.
This logic transpiles(TM) to this in my brain:
a) I am messing around and need to write 10 lines of code. Can I write it fast and without thinking? Sure and not needing to type int/float/whatever will save me couple of seconds. If I iterate and rewrite that short piece 10 times then I just saved 20 seconds. Chirp chirp ... . Do I need special language for just that? Lemme guess ...
b) I am messing around and need to write few hundred or thousands lines of code. Can I write it fast? Maybe but it is likely that good chunk of time will be spent thinking. I doubt that at this point not declaring type will save anything worth noticing.
But that of course is my opinion
Typing speed is only one constraint that type systems enforce. They also make it much slower to change input or output data from functions. I tend to use dynamic languages for projects between 100-500 loc and usually I’m not really sure what the final design will look like so need to try a lot of different ideas as fast as possible.
