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Matt Godbolt sold me on Rust by showing me C++

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611 points LorenDB | 1 comments | 06 May 25 17:51 UTC | HN request time: 0s | source
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simpaticoder ◴[06 May 25 23:10 UTC] No.43910617[source]▶
I don't get it. Isn't this a runtime problem and not a compile-time problem? buy() or sell() is going to be called with dynamic parameters at runtime, in general. That is, calls with concrete values are NOT going to be hard-coded into your program. I would write the function to assert() invariants within the function, and avoid chasing compile-time safety entirely. If parameter order was a concern, then I'd modify the function to take a struct, or similar.
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brundolf ◴[06 May 25 23:27 UTC] No.43910710[source]▶
> Isn't this a runtime problem and not a compile-time problem? buy() or sell() is going to be called with dynamic parameters at runtime, in general.

Yes, but the strength of Rust's type system means you're forced to handle those bad dynamic values up front (or get a crash, if you don't). That means the rest of your code can rest safe, knowing exactly what it's working with. You can see this in OP's parsing example, but it also applies to database clients and such

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simpaticoder ◴[07 May 25 00:07 UTC] No.43910929[source]▶
What if the valid input for quantity must be greater than 0? A reasonable constraint, I think. The OP's example is contrived to line up with Rust's built-in types, and ignores the general problem.
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1. brundolf ◴[07 May 25 05:47 UTC] No.43912604[source]▶
It's a common fallacy to equate "there's a limit to how much we can guarantee" with "guaranteeing anything is a waste of time". Each guarantee we can make eliminates a whole class of possible bugs

That said, Rust also makes it very easy to define your own types that can only be constructed/unpacked in limited ways, which can enforce special constraints on their contents. And it has a cultural norm of doing this in the standard library and elsewhere

Eg: a sibling poster noted the NonZero<T> type. Another example is that Rust's string types are guarantees to always contain valid UTF-8, because whenever you try and convert a byte array into a string, it gets checked and possibly rejected.