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Lesson I learned today: imperative languages can't express data structures that are both immutable *and* circular. For example, you can't build an immutable, doubly linked list in #csharp without ugly runtime assertions. 🤮Permalink On twitter.com
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Mood -3 🙁
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The reason for this is because you can't construct an immutable object without having all its dependencies first. So if A <-> B, you can't construct A without B, but you also can't make B without A.Permalink On twitter.com
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Mutability works around this because you can just construct A without a reference to B (such asPermalink On twitter.com
null) then add it later once you've made B. This made me wonder, are there other languages which can provide a compiler-guaranteed immutable *and* circular data structure? 🤔
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Like most esoteric #ComputerScience problems, the answer is: functional programming languages. For example, #Haskell does this by "tying the knot", leveraging laziness to define two symbols that reference each other. 🤯 wiki.haskell.org/Tying_the_KnotOn twitter.com
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You can use delegates to kind of do the same thing in #csharp, but it's still mutating state and the compiler doesn't understand it like #Haskell does. I don't really have a point to make here, just sharing some interesting stuff I learned today.Permalink On twitter.com
Mood +6 🙂