>
>
> Hello swift-evolution,
>
>
> There are clearly weaknesses with obtaining values from a given dictionary in
> swift. Most notably, if we have a [String: Any] dictionary, how is one
> supposed to set/get a value with type safety? The following concept addresses
> this very issue.
>
>
>
> I regularly use a self-constructed structure with static constants embedded
> within it, the structure enables a type safe implementation of keys and
> values (especially Dictionary applications). I will include a code snippet
> later on in this message, but I would specifically like to describe the
> benefits of a type safe key and value system, and how it would benefit the
> language.
>
>
>
> When using dictionaries in Swift, one often finds themselves needing to use
> more general key and value types (e.g. [String: Any]). Unfortunately, when a
> Dictionary uses a general type, rather than one with more type safety and
> compile time checks, many issues can arise from such a use case.
>
>
>
> The solution, in my opinion, is to use a pairing struct which can be used to
> create constant type-safe-enforcing structures. Additionally, said struct
> could have the ability to transform values of one type to that of another.
> Please see the code snippet below for more information regarding the
> implementation.
>
>
>
> >
> >
> > struct Bar {
> >
> > var str: String
> >
> > }
> >
> >
> >
> > var foo = [String: Any]()
> >
> > foo["bar"] = Bar(str: "Hello, world.")
> >
> >
> >
> > // We are optionally casting this value of `Any` to `Bar`, but it's
> > strongly typed, so there are clearly drawbacks.
> >
> > if let bar = foo["bar"] as? Bar {
> >
> > bar.str
> >
> > }
> >
> >
> >
> > // What if we use a `KeyValuePair`?
> >
> > let barPair = KeyValuePair<String, Any, Bar>(key: "bar")
> >
> > barPair.addValue(Bar(str: "This is better."), to: &foo)
> >
> >
> >
> > // Now look how easy (and safe) it is to get the value.
> >
> > let bar = barPair.value(from: foo)
> >
> >
>
>
> I have already implemented the underlying structure for the above example
> usage. Also, there are other use cases that are not highlighted here, such as
> built in value transformation.
>
>
>
> Let me know if anyone else agrees that this is a type safe solution for
> generalized dictionaries, or if think there are other uses for it. I also
> have all the code for the struct KeyValuePair, if anyone wants to see how it
> works, but it’s quite lightweight.
>
>
>
> Thank you,
>
>
>
>
>
>
>
>
>
>
> David Moore / Owner / Chief Executive Officer
> [email protected] (mailto:[email protected]) / (705) 845-6057
>
>
>
> Moore Development
> https://www.mooredev.ca
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
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