Thank you, Brent. But for me you just described a serialization to/from
string ;)
So, using your example, if I have
struct A: CustomStringConvertible {
var a = 0, b = 0
var description: String { return "a:\(a) b:\(b)" }
}
and I want to use it in your code. Will I be able to do this?
For example, I'm ok to give it 'lossless' representation as "\(a)/\(b)"
(i.e. 1/2 for example) and provide init() for string of such format.
I.e. it seems like I just should create extension and conform to
LosslessStringConvertible, but as I understand I can't, as I need not only
introduce an init(:String), but modify `description` property ?
I.e. assume you have no rights or don't want to modify the A type itself.
This is why I don't understand why we should have the same .description for
this LosslessStringConvertible(i.e. if it will be .loslessDescription - no
problems).
Most likely I don't understand something.
Also there is a question regarding your example: what to do with Double
type? We can have some configuration items of Double type, but how to use
this LosslessStringConvertible here?
On 31.05.2016 0:22, Brent Royal-Gordon wrote:
I can't understand this. For me ValuePreservingStringConvertible usually will
be different than CustomStringConvertible. Can't I want to have some string
view of my struct to present data(also in UI) *and* value preserving string
value for the same struct?
So my .description will show something like "12.345-6.78" and value preserving string
will contain something like "19083749347923847293487293483" to encode the data of the
struct. No?
Rather than thinking of LosslessStringConvertible as a protocol for serializing
data into a string, think of it as a protocol for those cases where the
human-readable description is also parseable and can be used to completely
recreate the instance. It's something you would use for things like
command-line arguments, environment variables, interactive command-line
programs, and configuration files that you expect humans to read and write by
hand.
func prompt<T: LosslessStringConvertible>(for field: String, of type:
T.Type) -> T {
while true {
print("What's your \(field)?")
let line = readline()
if !line.isEmpty
let value = T(line) { // how the hell
do you indent this stupid syntax?
return value
}
}
}
let name = prompt(for: "name", of: String)
let age = prompt(for: "age", of: Int)
let answer = age < 13 ? " not" : ""
print("\(name), you are\(answer) too old to have a favorite color.")
In other words, write the `description` first, and then decide if you can write
a good `init(_ description:)` to match it.
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