Correct me if I'm wrong, but this idea with accessors is not the same as
static properties for each case. The one of ideas of initial proposal -
static(!) values would be created only once and it is important in case it
is expensive to create such value(or if should be created only once per case)
The suggested solution based on 'accessor' - will create assotiated
properties each time the enum instace created, for each instance of enum type.
We can have something like the example with accessors now :
enum MyError: ErrorProtocol {
struct MyErrorInfo {
let localizedFailureReason: String
let url: String
}
case fileNotFound(url: String)
case fileIsCorrupt(url: String)
var info : MyErrorInfo {
switch self {
case fileNotFound(let url) : return
MyErrorInfo(localizedFailureReason: "File \"\(url.lowercased())\" not
found.", url: url)
case fileIsCorrupt(let url) : return
MyErrorInfo(localizedFailureReason: "File \"\(url.lowercased())\" is
corrupt.", url: url)
}
}
}
var e = MyError.fileNotFound(url: "http://something.some";)
var info = e.info
print(info.localizedFailureReason, info.url)
But yes, such MyErrorInfo will be created on each `info.` call. This is
worse that create MyErrorInfo once per each enum instance initialization,
but IMO these solutions are close enough.
In any case, I don't see why tuple for enum and enum with `accessor` can
not co-exists.
On 27.05.2016 2:28, Charles Srstka via swift-evolution wrote:
On May 26, 2016, at 4:47 PM, Brent Royal-Gordon via swift-evolution
<swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:
- Abusing rawValue is just that: an abuse.
In addition, enums with associated types can’t have rawValues.
Why is this relevant, you may ask? Because error enums are a huge use case
for something like this. Being able to do the below would be great:
enum MyError: ErrorProtocol {
accessor var localizedFailureReason: String
accessor var url: NSURL
case FileNotFound(url: NSURL) {
self.localizedFailureReason = “File \"\(url.lastPathComponent ??
“”)\” not found.”
self.url = url
}
case FileIsCorrupt(url: NSURL) {
self.localizedFailureReason = “File \"\(url.lastPathComponent ??
“”)\” is corrupt.”
self.url = url
}
}
This would be much cleaner than the existing method of using a switch to
create a userInfo dictionary for creating an NSError to send to
-[NSApplication presentError:] and similar methods.
Charles
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