Ivan Uemlianin

There is an inescapable tradeoff between what a software technology can do (its abilities) and what you know for certain about what it does (its guarantees). For example: - Unicode is able to represent strings like `中文🌴`, but ASCII guarantees that all visible characters are exactly one byte. - Safe rust guarantees an absence of (certain kinds of) memory errors, but it isn't able to encode as many valid programs as unsafe rust can. - `map` can't do every computation a `foreach` loop can, but `map` always guarantees the output list is the same size as the input list. - Graphs can represent more kinds of data than DAGs, which represent more than trees, which represent more than lists. But DAGs are orderable, trees have at most one path between nodes, and lists guarantee one order. The tradeoff exists whether we're talking formats, data structures, languages, or tools. It's so fundamental because it's universal. Give me any software topic and I will give you an example of this tradeoff. What's causing this? There's a surprisingly simple mathematical explanation! Abilities correspond to `some` quantifiers over a set, while guarantees correspond to `all` quantifiers. `some` is "monotonically true" over the size of the set, meaning when we grow the set, it can flip from false to true but not from true to false. Conversely, `all` is monotonically false, meaning it can flip from true to false but not vice versa. In other words: to increase a technology's guarantees we need to "shrink the corresponding set", which by definition decreases its abilities. The ability-guarantee tradeoff is one of the running motifs of my book Logic for Programmers: not the subject of a chapter, but an idea that runs through many chapters. The tradeoff connects diverse topics like testing, optimization problems, and domain-driven design. If this interests you, the book is available in pdf, epub, and print formats. Check the link below! logicforprogrammers.com/ (Or, if you want to participate in the November charity drive, check out the link in the next Tweet!)