Comment by bryanrasmussen
14 days ago
whether something (a variable) is a width or a height is encoded somewhere in the code because if the variable is a width it makes its usage different than if it is a height.
Then the code is written to make sure you never make the mistake of sending a width to a height, because that would be silly.
The type (width or height) is represented as logic in the code.
theoretically - if you have a type system that allows you to know something is a width or height you can often reduce logic to keep track of these things but my experience is that level of granularity in your typing reduces dynamism too much. I would rather keep track of that in code (as it probably will have to deal with it anyway) than make my type system deal with it.
There's some cool mechanisms in type-forward languages that lead to minimal dynamism loss along with safety: For instance, you can do scientific programming that carries units along. So you really can divide a length by a time with no problems: Your results just happens to be a velocity, and will come out in meters per second (or whichever your favorite units are). Adding meters to kilometers? Congrats, you might you have to say which physical representation you want in float-land. But then you are saved from adding seconds to milliliters, because then the types will tell you it's complete nonsense.
But note that to make all of that work well you really need your language to provide a lot of syntactic sugar features which are missing in most older languages, so all the operations read seamlessly, instead of being full of ceremony. One could do all of this in, say, old Java 1.4 or something, but the amount of type annotation, along with the massive mounts of boilerplate to get all of the operationg working right, and checked at compile time would make it all Not-Worth-It(tm) But with enough language features, and a smart enough compiler, `val acc = mySpeed / someSeconds` will work, straight up, with the safety included.
thanks for saying it a lot better than I did!
> But then you are saved from adding seconds to milliliters, because then the types will tell you it's complete nonsense.
I was thinking about this as I was reading your comment, and wondering: is it nonsense? If I have 5 seconds of time as well as 10 milliliters of water... I can consider them as being packaged together... which is addition. And I can subtract 3 milliliters and 6 seconds from them without running out of what I had. Nothing wrong with that, really. Five potatoes and a gallon of water is the same notion, just more familiar. Seems no more nonsensical than dividing length by time, right? Food for thought...
Bundling the time and the volume might be better called "forming a vector" or "forming an ordered pair" rather than "addition". You can then perform addition and subtraction with the resulting ordered pairs or vectors.
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That's nonsense because addition loses the structure. 3 litres and 6 seconds becomes indistinguishable from 4 litres and 5 seconds. Maybe that's what you want, but it's realistically pretty much never what you want.
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