[swift-evolution] [swift-evolution-announce] [Review] SE-0023 API Design Guidelines

David Owens II david at owensd.io
Sun Jan 24 18:53:40 CST 2016

>> I guess my point is this: codifying a convention seems pre-mature as
>> that convention doesn't bring the safety goals of the language into a
>> place that's verifiable. All of the other guidelines are simply about
>> clarity of use, this convention has a far reaching impact.
> Sorry, could you clarify what you mean by "bring the safety goals of the
> language into a place that's verifiable" and clarify why having a "far
> reaching impact" would somehow conflict with being "about clarity of use?"
> It seems to me that this convention is about how to express whether a
> method is going to mutate so it's clear at the use-site.  What am I
> missing?

The problem is it's unclear to me whether you mean mutate in the true sense of the word or only applied to a struct with a function annotated with the mutating keyword.

The naming convention provides no safety when dealing with non-struct types as we cannot enforce that a method on a class does not mutate it's internal members.

That's the clarity I'm looking for.

Given this API set:

protocol InPlaceable {
    mutating func doInPlace()

public struct Foo: InPlaceable {
    mutating func doInPlace() {}

public class Bar: InPlaceable {
    func doInPlace() {}

var lie: InPlaceable = Bar()

let lie2 = Bar()

The convention will tell us a lie unless we are extremely careful. It's this lie that concerns me. We cannot guarantee that the "doInPlace" truly matches the definition we are seeking.

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