Hi Ole,
> On Dec 5, 2016, at 5:11 AM, Ole Begemann via swift-corelibs-dev
> <swift-corelibs-dev@swift.org> wrote:
>
> (Apologies if this is not the right list to ask this question. I couldn't
> decide between swift-corelibs-dev and swift-dev.)
>
> I noticed that the NSArray and NSDictionary initializers to create a
> collection from a property list file are not exposed in the stdlib Array and
> Dictionary types. The same is true for the corresponding methods to write a
> collection to a property list:
>
> – init?(contentsOfFile:)
> – init?(contentsOfURL:)
> – write(toFile:atomically:)
> – write(to:atomically:)
>
> You can still call these from Swift by using NSArray or NSDictionary directly.
>
> My question is why this decision was made, purely out of interest and because
> I couldn't find any information about this. I can imagine a few reasons:
>
> 1) Property lists are quite specific to Apple platforms and we don't want to
> "pollute" the standard library with platform-specific solutions.
>
> 2) Plists are just one of several potentially useful file formats and users
> might assume that an initializer to deserialize a collection from a file also
> supported other file formats, such as JSON or YAML, especially with a generic
> name like init(contentsOfFile:).
>
> 3) The resulting collections are heterogeneously typed ([Any] or
> [String:Any]) and as such not very pleasant to work with in Swift, so Array
> and Dictionary are really considered to be the wrong types to offer this
> functionality. It would be preferable to have a separate data type for
> working with plists, something like:
>
> enum PropertyList {
> case text(String)
> case bool(Bool)
> case int(Int)
> case double(Double)
> case date(Date)
> indirect case array([PropertyList])
> indirect case dict([String: PropertyList])
> }
>
> Thanks!
> Ole
>
The main reason is actually that we just prefer people use
NSPropertyListSerialization API to read or write property lists. One big
reason: that API has the possibility of giving you an error, whereas the
collection methods do not.
The collection API is a trivial convenience method over property list
serialization anyway. Here is the implementation:
data = [[NSData allocWithZone:NULL] initWithContentsOfFile:path];
if (!data) return nil;
id plist = [[NSPropertyListSerialization propertyListWithData:data
options:immutable ? NSPropertyListImmutable : NSPropertyListMutableContainers
format:NULL error:NULL] retain];
[data release];
Plus an additional check to make sure the result is the right type (array or
dictionary).
- Tony
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