I am using Scala IDE on Mac (Build id: 4.4.1-vfinal-2016-05-04T11:16:00Z-Typesafe) with Scala 2.11.8. I have a trait defined as below:
package services
trait UserSignupService {
def signupUserByCellphone(cellphone: String) : Future[Boolean]
def isExistingUser(providerId: String, providerKey: String): Future[Boolean]
def createUser(providerId: String, providerSignupToken: String)
def verifySignupToken(providerId: String, providerSignupToken: String): Future[Boolean]
}
and a class:
package services.impl
#Singleton
class UserSignupServiceImpl extends UserSignupService {
}
When I press CMD-3 and choose override implement methods I do not see the methods for the trait defined above. I only see methods from java.lang.object.
Build automatically is selected and enabled. I also tried cleaning the project but it just doesn't work.
If I type in the method name and press ctrl-space it gives me the correct suggestion:
What's going on? What am I missing?
Ah. I found the answer. The feature is not supported in Scala IDE. As per this post in google groups
"This feature "override/implement methods" is a feature provided by
the Java editor, it has no knowledge about Scala. Since the Scala
editor inherits functionality from the Java editor, this functionality
is shown. We could probably override the implementation with our own
but so far we didn't. By pressing CMD-1 (the key combination for quick
assists), you should get a list with methods to implement. This is a
little bit more cumbersome but works."
Related
I see, that it's defined in Interface IntStream, but when you write IntStream.range(0, 200).sum(); how the implementation is called? where is it? couldn't find..
As for every interface, it's defined in the concrete class(es) that implement the interface.
In this case, it's in java.util.stream.IntPipeline, which is not a public class. But you shouldn't care about that. All you need to know is that an IntStream has that method, which does what the javadoc of the method does.
If you're really curious about its implementation, look in the source code of IntPipeline.java:
return reduce(0, Integer::sum);
Note on how I found out extremely easily: I just open the type hierarchy of IntStream in my IDE (IntelliJ, but all decent IDEs have that functionality), and notice that it has a single direct implementation: IntPipeline, which indeed contains the method.
If you are using an eligible compiler, there is an option to show its implementation. For example, when I want to see its implementation by IntelliJ, I click go to implementation. Then, it redirects.
In IntPipeLine.java,
#Override
public final int sum() {
return reduce(0, Integer::sum);
}
Suppose we have some data classes which are generated with protoc.
Google's toString() sucks for multiple reasons, it's not very human-readable, and even puts line breaks in representation which screws up logs and many tools that don't expect multiline log.
So the problem is: how do we redefine custom toString() for a class like that?
I've tried to override (or maybe hide?) original toString() with an extension function like this
fun Messages.DataClass.toString(): String {
return "some custom logic"
}
but it won't pick up the extended function.
It's not possible to change the implementation of an existing method in a class using Kotlin. An instance method defined in a class always takes priority over an extension function with the same signature.
I need to write a Spotlight Importer for an application that I've written in Swift, and am referring to the official Apple guide for Writing a Spotlight Importer.
It seems straightforward enough, however creating a Spotlight Importer project creates a default setup for an Objective-C implementation. Now, working with Objective-C isn't a huge problem (I've used it plenty of times in the past) but everything I've written for my application is in Swift, so I'd really I'd like to write the importer in Swift too to avoid switching between languages, and also so I can share some of the code that I've already done for reading/writing files.
Firstly, is it possible to write a Spotlight Importer using Swift instead of Objective-C? And if it is, where should I start (e.g- if I take the Objective-C starting point, what would I do to switch over to Swift instead)?
It took me a bit of time to get this to work.
Instead of adding Swift code to the mdimporter, I import an embedded framework already setup for my app.
I removed all the example code except main.c and GetMetadataForFile.m.
In the latter I import my framework where all the functionality now resides as Swift code.
The built mdimporter is added to the app.
In the File Inspector set Location to Relative to Build Products.
The app then adds the mdimporter with a Copy Files Build Phase.
Destination: Wrapper
Subpath: Contents/Library/Spotlight
The following needs to be added to the Run Search Paths build setting, as we are linking to the app's embedded frameworks.
#loader_path/../../../../../Frameworks
If you get compiler error that the framework module can't be found when building the app, depending on how your workspace is set up, you might need to modify your app's Scheme.
Turn off Parallelize Build
Add the Build targets in this sequence:
Frameworks project(s)
mdimporter project
App project
The additional benefit of having all the logic in a framework, is that it can be prototyped and verified in a Playground. A million times easier than debugging an mdimporter plugin.
Yes, it is possible to write a Spotlight Importer entirely* in Swift!
*except for a few lines of code in main.m
I've just published one here: https://github.com/foxglove/MCAPSpotlightImporter
Here's a detailed blog post about the implementation process:
https://foxglove.dev/blog/implementing-a-macos-search-plugin-for-robotics-data
The difficult part of this is implementing a plugin that's compatible with the CFPlugIn architecture. (The MDImporter-specific logic is relatively minimal.) The CFPlugIn API is based on Microsoft's COM and Apple's docs are almost 20 years old.
The plugin is expected to be a block of memory conforming to a certain memory layout — specifically, the first value in the block must be a pointer to a virtual function table (vtable) for the requested interface (in the case of a MDImporter, this is either MDImporterInterfaceStruct or MDImporterURLInterfaceStruct) or the base IUnknown interface. This layout is documented here.
I wanted to organize the Swift code into a class, but you can't control the memory layout of a Swift class instance. So I created a "wrapper" block of memory which holds the vtable and an unsafe pointer to the class instance. The class has a static func allocate() which uses UnsafeMutablePointer to allocate the wrapper block, create and store the class instance in it, and also initialize the vtable.
The vtable implements the standard COM base interface (IUnknown) functions (QueryInterface, AddRef, and Release) by grabbing the class instance out of the wrapper and calling the queryInterface(), addRef(), and release() methods on the instance. It also implements the Spotlight-specific ImporterImportURLData function (or ImporterImportData). Unfortunately, in my testing, it seemed like Spotlight did not pass the correct pointer to the wrapper struct as the first argument to ImporterImportURLData, so it was impossible to call a method on the class instance, so the function that actually imports attributes for a file had to be a global function. For this reason I wasn't able to make the plug-in implementation a more generic class that could be used with any interface — it has to be tied to a specific global importer function.
I'd encourage you to view the full source on GitHub, but in the interest of not being a link-only answer, here's the core functionality:
final class ImporterPlugin {
typealias VTable = MDImporterURLInterfaceStruct
typealias Wrapper = (vtablePtr: UnsafeMutablePointer<VTable>, instance: UnsafeMutableRawPointer)
let wrapperPtr: UnsafeMutablePointer<Wrapper>
var refCount = 1
let factoryUUID: CFUUID
private init(wrapperPtr: UnsafeMutablePointer<Wrapper>, factoryUUID: CFUUID) {
self.wrapperPtr = wrapperPtr
self.factoryUUID = factoryUUID
CFPlugInAddInstanceForFactory(factoryUUID)
}
deinit {
let uuid = UUID(factoryUUID)
CFPlugInRemoveInstanceForFactory(factoryUUID)
}
static func fromWrapper(_ plugin: UnsafeMutableRawPointer?) -> Self? {
if let wrapper = plugin?.assumingMemoryBound(to: Wrapper.self) {
return Unmanaged<Self>.fromOpaque(wrapper.pointee.instance).takeUnretainedValue()
}
return nil
}
func queryInterface(uuid: UUID) -> UnsafeMutablePointer<Wrapper>? {
if uuid == kMDImporterURLInterfaceID || uuid == IUnknownUUID {
addRef()
return wrapperPtr
}
return nil
}
func addRef() {
precondition(refCount > 0)
refCount += 1
}
func release() {
precondition(refCount > 0)
refCount -= 1
if refCount == 0 {
Unmanaged<ImporterPlugin>.fromOpaque(wrapperPtr.pointee.instance).release()
wrapperPtr.pointee.vtablePtr.deinitialize(count: 1)
wrapperPtr.pointee.vtablePtr.deallocate()
wrapperPtr.deinitialize(count: 1)
wrapperPtr.deallocate()
}
}
static func allocate(factoryUUID: CFUUID) -> Self {
let wrapperPtr = UnsafeMutablePointer<Wrapper>.allocate(capacity: 1)
let vtablePtr = UnsafeMutablePointer<VTable>.allocate(capacity: 1)
let instance = Self(wrapperPtr: wrapperPtr, factoryUUID: factoryUUID)
let unmanaged = Unmanaged.passRetained(instance)
vtablePtr.initialize(to: VTable(
_reserved: nil,
QueryInterface: { wrapper, iid, outInterface in
if let instance = ImporterPlugin.fromWrapper(wrapper) {
if let interface = instance.queryInterface(uuid: UUID(iid)) {
outInterface?.pointee = UnsafeMutableRawPointer(interface)
return S_OK
}
}
outInterface?.pointee = nil
return HRESULT(bitPattern: 0x8000_0004) // E_NOINTERFACE <https://github.com/apple/swift/issues/61851>
},
AddRef: { wrapper in
if let instance = ImporterPlugin.fromWrapper(wrapper) {
instance.addRef()
}
return 0 // optional
},
Release: { wrapper in
if let instance = ImporterPlugin.fromWrapper(wrapper) {
instance.release()
}
return 0 // optional
},
ImporterImportURLData: { _, mutableAttributes, contentTypeUTI, url in
// Note: in practice, the first argument `wrapper` has the wrong value passed to it, so we can't use it here
guard let contentTypeUTI = contentTypeUTI as String?,
let url = url as URL?,
let mutableAttributes = mutableAttributes as NSMutableDictionary?
else {
return false
}
var attributes: [AnyHashable: Any] = mutableAttributes as NSDictionary as Dictionary
// Call custom global function to import attributes
let result = importAttributes(&attributes, forFileAt: url, contentTypeUTI: contentTypeUTI)
mutableAttributes.removeAllObjects()
mutableAttributes.addEntries(from: attributes)
return DarwinBoolean(result)
}
))
wrapperPtr.initialize(to: (vtablePtr: vtablePtr, instance: unmanaged.toOpaque()))
return instance
}
}
Finally, I created an #objc class that exposes this allocate function to Obj-C, where I can call it from main.m, and return the pointer to the wrapper block from the factory function. This was necessary because I didn't want to use the unstable #_cdecl attribute to expose a Swift function directly to the plug-in loader.
#objc public final class PluginFactory: NSObject {
#objc public static func createPlugin(ofType type: CFUUID, factoryUUID: CFUUID) -> UnsafeMutableRawPointer? {
if UUID(type) == kMDImporterTypeID {
return UnsafeMutableRawPointer(ImporterPlugin.allocate(factoryUUID: factoryUUID).wrapperPtr)
}
return nil
}
}
// main.m
void *MyImporterPluginFactory(CFAllocatorRef allocator, CFUUIDRef typeID) {
return [PluginFactory createPluginOfType:typeID factoryUUID:CFUUIDCreateFromString(NULL, CFSTR("your plugin factory uuid"))];
}
See my blog post for more details.
Since Apple introduced Swift as a language to be perfectly compatible with any existing Objective-C project I would suggest you just start with whatever makes things easier for you.
If you know Swift best then nothing keeps you from using that – for whatever project you might want. If you want to follow a tutorial that was written for Objective-C and not updated for Swift yet, I think you have two choices (I'd personally recommend going for the second option for now):
Write the same logic written in Objective-C within the tutorial now in Swift from scratch (nearly everything possible in Objective-C is easily possible with Swift, too). For that you need to understand the basics of Objective-C and the corresponding syntax and features in Swift though.
Start with Objective-C to follow the tutorial and keep things easier at the beginning (no need to really understand the tutorials details). Then use the great possibility of mix and matching Swift code alongside Objective-C code to customize the code for your needs or to extend it with your own pre-existing classes.
More specifically on the second option:
If you want to write new classes just use Swift – you can perfectly use everything written in Objective-C from within Swift and vice versa. If you feel you need to change classes already written in Objective-C you have these options: Extend the class written in Objective-C with a new Swift class, re-write that specific file in Swift or just edit the Objective-C file directly.
To learn more on how to mix and match Swift code alongside Objective-C I recommend reading Apples official documentation. It's part of the free iBook "Using Swift with Cocoa and Objective-C" written by Apple engineers for developers.
Unfortunately Apple actually does seem to provide their template for a Spotlight Importer from within XCode for Objective-C only at the moment. Don't know why this is though – I can't see anything stopping them from supporting Swift. We should probably report this with Apples Bug Reporter to stress the fact that people are actually asking for this.
Hope I didn't overlook anything here, otherwise my answer will be pointless. ^^
UPDATE (request)
Here are some steps on where to begin to implement the first approach:
First create a Spotlight Importer project with the latest XCode version
– Create a new "Cocoa Touch" class named exactly the same as your pre-created main Objective-C classes (e.g. "MySpotlightImporter")
Choose Swift and "Create Bridging Header" when asked during class creation
– Re-implement the code written in the ObjC-MySpotlightImporter class within the Swift class (you might want to create a Cocoa App with Core Data support in Swift and Objective-C to get some idea of their differences)
– I'm not sure if you can rewrite the GetMetaDataFile.m in Swift, too, I couldn't figure that out in my test, so you maybe need to keep it around (for now)
– In case you receive any errors along the way that point to some missing configuration just search for the related files/classes in the projects "Build settings" and apply your changes there
I hope this helps to get you started and is specific enough. I tried to do the necessary changes myself in order to provide an example project in Swift but unfortunately I couldn't get it working in a limited time. You may want to consider providing your code publicly though (e.g. on GitHub with a link posted here) in case you decide to port it yourself so others can profit from this, too.
Good luck!
If I don't know there exists an interface or method in Java and I have to write one by my own.
How can I avoid this? (It takes much more time to write a method by myself.) How can I find a method which I even don't know the name of it?
Q: Are you worried that you might create an interface or method with a duplicate name?
If so, the answer is to use "packages"
EXAMPLE:
package com.mypackage;
interface myInterface {
public void myMethod ();
}
Here is a good tutorial:
http://docs.oracle.com/javase/tutorial/java/package/packages.html
I'm working to learn Scala--coming from a C++ background. I am trying
to write a small class for a task tracking app I'm hacking together to
help me to learn how to code Scala.
This seems as if it should be simple but for some reason it's eluding me:
package com.catenacci.tts
class Task(val ID:Int, val Description:String) {
val EmptyID = 0
val EmptyDescription = "No Description"
def this() = this(EmptyID,EmptyDescription)
def this(ID:Int)={
this(ID,EmptyDescription)
}
def this(Description:String)={
this(EmptyID,Description)
}
}
I'm trying to provide three constructors: Task(ID, Description),
Task(ID), Task(Description). In the latter 2 cases I want to
initialize the values to constant values if one of the values isn't
provided by the caller. And I want to be able to check this outside
of the class for unit testing purposes. So I figured putting in two
public vals would allow me to check from outside of the class to make
sure that my state is what I expect.
However, for some reason this code will not compile. I get the following error:
error: not found: value EmptyID
and
error: not found: value EmptyDescription
So what am I missing? I'm working through "Programming in Scala" so
if there's a simple answer to this question, please give me page
numbers. I don't mind reading but going by the code on page 60 and
page 62, I can't see why this code is failing.
I'm guessing it has something to do with the fact that these are
constructor methods and that possibly the two vals are not initialized
until the end of the constructors. If that's the case is there some
way to get the effect I'm looking for?
You can define the constants in a companion object:
object Task {
val EmptyID = 0
val EmptyDescription = "No Description"
}
And then reference them as Task.EmptyID and Task.EmptyDescription.
I think Scala 2.8 has support for default values.
See Germán for the answer. This happens because a constructor is technically part of the static scope. In other words, the constructor cannot access any instance members because the instance hasn't been created yet. Any "class members" are actually instance members, which is why the code in the question does not work. Germán's answer fixes this by moving the two relevant values into the companion object, which effectively makes them static members of the Task class (not really, but you can think of it that way).
In "Programming in Scala", see section 6.7 where the chaining of constructor calls is explained. The primary constructor is described as "the single point of entry of a class".