Greetings — I haven't found this specific topic in the archives; apologies
if this has come up before.
Suppose I have a C struct with an embedded char array:
struct fileinfo_t {
char path[256];
};
and I want to convert the path to a Swift String (in order to implement
`description`, say). I would like to use String.init(cString:) for this;
but the `path` field is imported as a tuple of 256 `Int8`s, and I need to
get an `UnsafePointer<CChar>`.
So I would like to write something like this:
extension fileinfo_t: CustomStringConvertible {
public var description: String {
let path = withUnsafePointer(to: &self.path) {
$0.withMemoryRebound(to: CChar.self, capacity:
MemoryLayout.size(ofValue: self.path) {
$0
}
}
return "fileinfo_t: \(path)"
}
}
The problem is that `self.path` is immutable, so I can't pass it to the
inout parameter of `withUnsafePointer(to:)`, even though its value is never
modified. I can either (1) write the `description` accessor as `mutating
get` — but then it no longer conforms to `CustomStringConvertible` — or (2)
copy the `path` field into a local `var` that can be passed to
`withUnsafePointer(to:)`, and hope that the compiler can optimize away the
copy.
In the absence of the Swift 4 ownership model (with which I presume this
could be marked as a borrowed reference), is (2) the best I can do for
now? And is this the sort of issue that the Ownership Manifesto is
designed to address?
Thanks,
— Russell Finn
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