[swift-evolution] Localization support for string interpolation

Erica Sadun erica at ericasadun.com
Mon Apr 25 21:29:25 CDT 2016

> On Apr 25, 2016, at 7:15 PM, Brent Royal-Gordon via swift-evolution <swift-evolution at swift.org> wrote:
>> I believe I also had concerns about this design because it needlessly
>> misses opportunities for compile-time type safety.  There doesn't seem
>> to be any reason to embed the format specifier in a dynamic string that
>> has to be parsed at runtime.
> I started drafting a post yesterday making the same point, but got bogged down in writing an example of what I *would* want to see.
> In brief: printf()-style specifiers are kind of awful. They're very cryptic and unnecessarily unsafe. In C, this problem is addressed by compiler warnings, but Swift already has a mechanism to detect inappropriate combinations of data and operations: the type system. We should use it here.
> If we had a protocol to handle formatting, I would want the method's parameter to be of an associated type and typically be something OptionSet-like. It might even be better to structure it as some sort of Formatter protocol. If properly designed, this might allow us to leverage Foundation's existing, fully-featured formatters rather than writing new ones just for Swift.

Keep in mind that succinctness is a virtue, especially when using embedded annotations. (I really liked your first go at this)
Also leveraging training and experience using the (ugly but) time-tested shorthand form is not necessarily bad. The safety
issue comes more in matching types, not in doing something like \(foo.#(%06.1f))

-- E

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