[Libre-soc-misc] Rust & correctness

Jacob Lifshay programmerjake at gmail.com
Fri Dec 18 22:16:53 GMT 2020

On Fri, Dec 18, 2020, 13:35 Luke Kenneth Casson Leighton <lkcl at lkcl.net>

> On Friday, December 18, 2020, Jacob Lifshay <programmerjake at gmail.com>
> wrote:
> > The article compares/contrasts the http libraries from NodeJS,
> yyeah that's about as helpful as comparing a plastic kid's bow and arrow
> to a Sherman Tank and saying, "but look, they're both weapons, no really!"

Umm, Go (one of the languages used as a bad example of API design) is
strongly typed last I checked...

> however even there, the analogy is broken and flawed: making comparisons
> of strongly typed languages against polymorphic ones then effectively
> saying "strong typed languages are automatically better" entirely and
> completely misses the benefits of both.

They do mention that languages such as JavaScript (& Python) are promoted
based on the speed you can write an initial implementation, just that you
require tons of tests and keeping different parts in sync and properly
tested is a huge chore.

The essay is taking the position that you may have an initial
implementation faster, but all the testing and bug fixing will take more
time than just having written it in a language like Rust with better API
design in the first place.

Rust, by contrast, encourages APIs such that most of the properties you'd
need huge piles of tests for in traditional languages are automatically
enforced by the compiler by using a good API design.

polymorphic languages have the huge advantage of being able to satisfy the
> Liskov Substitution Principle *without* the need for the base class, older
> (prior-written) or newer code to even know that the new variant satisfying
> the LSP is even being used.

I would argue that that is often a disadvantage, because of the API
interface being declared mostly in documentation which can easily be
inconsistent, incomplete, out-of-date, or just plain missing. This forces
libraries to avoid changing their implementation to avoid breaking code
that was using part of what they thought was public API surface, but was
intended to be private. A good example of why Rust's explicit
compiler-visible typing, combined with good API design, allows for complete
substitution of the implementation is Rust's standard library recently
completely replacing their hashmap implementation with a totally different,
much faster (often faster than even C++), implementation.

> where for strong declarative languages, due to the strict typing it is
> simply impossible to deploy LSP.... *unless the programmer has planned for
> that in advance* at the base level of the API.

Rust makes it very easy to deploy something like safe type-checked LSP,
when desired, by using generics and traits (which are waay more powerful
and flexible than base classes, and much harder to accidentally misuse than
C++ templates). Quite a lot of rust code does that, btw. It also supports
opt-in dynamic dispatch.

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