Sorry if this is a real basic question, am relatively new to scala
I am trying to make 2 class which are Disease and Cancer where Cancer class extends the Disease class
class Disease ( diseaseNameS : String, symptomsS : String, recommendMedS : String ){
var diseaseName = new StringProperty(diseaseNameS)
var symptoms = new StringProperty(symptomsS)
var recommendMed = new StringProperty(recommendMedS)
}
class Cancer ( diseaseNameS : String, symptomsS : String, recommendMedS : String ) extends Disease (diseaseNameS, symptomsS, recommendMedS){
override var recommendMedS : String = "Chemotherapy"
}
object Disease {
val diseaseData = new ObservableBuffer[Disease]()
diseaseData += new Disease("Common cold", "Headache, Sore throat, Stuffy nose","Decongestants, Ibuprofen")
diseaseData += new Cancer("Prostate cancer", "Frequent urination", "Radical prostatectomy")
error:
Disease.scala:13:16: recommendMedS is already defined as value recommendMedS
[error] override var recommendMedS : String = "Chemotherapy"
What I want is when I print the diseaseData the "Radical prostatectomy" string in new Cancer will get overrided by "Chemotherapy". Am I doing this wrong?
A better solution to this specific problem is this:
class Cancer(diseaseNameS: String, symptomsS: String)
extends Disease(diseaseNameS, symptomsS, "Chemotherapy") {
}
This prevents someone from specifying a recommendedMed for Cancer because it is always "Chemotherapy".
I believe what you want is this:
class Cancer(diseaseNameS: String, symptomsS: String, recommendMedS : String = "Chemotherapy")
extends Disease(diseaseNameS, symptomsS, recommendMedS) {
}
This way you don't need to set recommendMedS for Cancer, and default "Chemotherapy" is used, but if you do set it, the set value is used.
Related
I'm relatively new to swift and searched around but could not find any satisfactory answer to my problem. I would like to have a Singleton class instance which can be initialized with some variables. E.g.
public class Singleton {
var car: String
var bus: String
init(car: String, bus: String) {
self.car = car
self.car = bus
}
func drive() {
print("I will drive")
}
}
public class SingletonConsumer {
// create an instance of Singleton Once
var driver: Singleton = Singleton(car: "honda", bus: "volvo")
driver.drive()
}
public class driverClassWorld : SingletonConsumer {
driver.drive()
}
how can i achieve it? I tried protocol but issue i am hitting is how to instantiate singleton class with parameters.
I don't get this problem?
First remove singleton from your brain for a moment. Because I think you have the wrong idea on what a singleton is.
Now lets rephrase your question to: "How to instantiate a class with parameter"
Its like this:
import Foundation
class Test {
let someText : String!
init(something:String){
someText = something
}
func test(){
print("TEST \(someText)")
}
}
let a = Test(something: "Me")
a.test()
Output:
TEST Optional("Me")
You just need to define a init with the parameters you want.
Now to properly instantiate a singleton (basically it just the class above but single instance). There are a lot of ways, the old Objective C approach is still valid.
But for swift this is the most common pattern. You need to define a Static Property.
Example:
import Foundation
class Test {
static let shared = Test(something: "REAL SINGLETON")
let someText : String!
init(something:String){
someText = something
}
func test(){
print("TEST \(someText)")
}
}
Test.shared.test()
Output:
TEST Optional("REAL SINGLETON")
Now reread the definition of a singleton:
a singleton class is a class that can have only one object (an
instance of the class) at a time
For other patterns in declaring a singleton:
https://cocoacasts.com/what-is-a-singleton-and-how-to-create-one-in-swift
Now, you might wonder: When does this singleton instance instantiated?
Answer: It is when it is first used/called.
I have written 2 codes .The functionality of both the code is same.Both the codes take user data then store it in map and on providing keys we get correspoding user data. I have written an extra logic in code2, whic I have mentioned below.
Code1:
class user(var name:String,var id:Int, var gender:Option[String])
{
override def toString="("+ name+","+id+","+gender+")"
}
object a
{
def main(args:Array[String]):Unit={
var a=new user("kl",90,Some("Male"))
println(a.name,a.id,a.gender)//ACESS VALUES
//DEFINING MAP
var mm=Map(1-> new user("jh",189,Some("Male")),2->new user("gh",12,None),3
->new user("io",100,Some("Female")))
// defining method giving o/p value of specific key of mm
def getkey(i:Int)=
{ mm.get(i)
}
var u1=getkey(readLine("ENTER THE KEY").toInt) // some[user]
println(u1.getClass.getName)
if(u1.isDefined)
{
println(u1.get+","+u1.get.name+","+u1.get.id+","+u1.get.gender)
}
}
}
Code1 1 works properly and O/P is right. I have added extra logic in Code2. The extra logic is getKey method. I have written a code for checking whether the input key is present in map. There I am getting an error:
**value get is not a member of java.io.Serializable**_
Code2:
class user(var name:String,var id:Int, var gender:Option[String])
{
override def toString="("+ name+","+id+","+gender+")"
}
object a
{
def main(args:Array[String]):Unit={
var a=new user("kl",90,Some("Male"))
println(a.name,a.id,a.gender)//ACESS VALUES
//DEFINING MAP
var mm=Map(1-> new user("jh",189,Some("Male")),2->new user("gh",12,None),3-> new user("io",100,Some("Female")))
// defining method giving o/p value of specific key of mm
def getkey(i:Int)=
{
//EXTRA LOGIC
var a=(mm.keys).toList
if(a.contains(i)){mm.get(i)}
else {"NO SUCH ELEMENT EXCEPTION , KEY DOESNT MATCH"}
}
print("ENTER THE KEY \n")
var u1=getkey(1) // some[user]
println(u1.get)
}
}
ERROR -
enter code here
eg1.Option.scala:27: error: value get is not a member of
java.io.Serializable
println(u1.get)
^
one error found
Why does the seriliazable errors occurs in Code2 and not in Code1? Is the error due extra logic in Code2? How to fix an error?
Thank you!
It happens because your getKey function return type is io.Serializable.
Reason for this is that every branch of your if expression is returning a different type:
def getkey(i:Int) = { // io.Serializable
//EXTRA LOGIC
var a=(mm.keys).toList
if(a.contains(i)) { mm.get(i) } // option here
else { "NO SUCH ELEMENT EXCEPTION , KEY DOESNT MATCH" } // string here
}
Consider rewriting your function, so its return type is Option[User], one way of doing so is:
def getkey(i:Int): Option[user] = {
//EXTRA LOGIC
var a=(mm.keys).toList
if(a.contains(i)) { mm.get(i) }
else { None }
}
However, there is no need for checking keys, you can simplify this function to:
def getkey(i:Int): Option[user] = {
//EXTRA LOGIC
m.get(i)
}
Hint: write expected return type for functions to see what's going wrong in such cases.
Seems like I'm having a problem with something that shouldn't be the case... But I would like to ask for some help.
There are some explanations here on the Stack I don't get.
Having two simple classes where one refers to another, as per below:
class User {
lazy var name: String = ""
lazy var age: Int = 0
init (name: String, age: Int) {
self.name = name
self.age = age
}
}
class MyOwn {
let myUser: User = User(name: "John", age: 100)
var life = myUser.age
//Cannot use instance member 'myUser' within property initializer
//property initializers run before 'self' is available
}
I get the commented compile error. May someone please tell me what should I do to solve the case?
As correctly pointed out by vadian you should create an init in such scenarios:
class MyOwn {
let myUser: User
var life: Int
init() {
self.myUser = User(name: "John", age: 100)
self.life = myUser.age
}
}
You can't provide a default value for a stored property that depends on another instance property.
You should declare life like this:
lazy var life:Int = {
return self.myUser.age
}()
Because you are trying to initialise one property(variable) with another during initialisation process. At this time variables are not available yet.
I want to assign properties to the instance of a class without knowing the property names, values and types of values in TypeScript. Lets assume we have the following example.ts script:
// This could be a server response and could look totally diffent another time...
const someJson:string = '{ "foo": "bar", "bar": "baz" }'
class MyClass {
someProperty:boolean
constructor( json:string ) {
const parsedJson:any = JSON.parse( json )
Object.keys( parsedJson ).forEach(
( key:string ) => {
this[ key ] = parsedJson[ key ]
}
)
this['someProperty'] = true
}
}
const myInstance = new MyClass( someJson )
// Works fine, logs `true`.
console.log( myInstance.someProperty )
// Error: Property 'foo' does not exist on type 'MyClass'.
console.log( myInstance.foo )
// Error: Property 'bar' does not exist on type 'MyClass'.
console.log( myInstance.bar )
How can I make sure that the TypeScript compiler does not complain of the dynamically added properties but instead handle them as "key": value pairs of any type. I still want tsc to make sure that myInstance.someProperty has to be of type boolean but I want to be able to get myInstance.whatever even if it is not defined without running into compiler errors.
I did not find any documentation that makes this clear to me. Maybe because I'm not a native english speaker. So please keep the answers simple.
Edit:
I remember that there was something like the following but I never got that to work:
interface IMyClass {
[name:string]: any
}
The problem is that you're adding the new properties at runtime and the compiler has no way of knowing that.
If you know the property names in advance then you can do this:
type Json = {
foo: string;
bar: string;
}
...
const myInstance = new MyClass(someJson) as MyClass & Json;
console.log(myInstance.foo) // no error
Edit
If you do not know the properties in advance then you can't do this:
console.log(myInstance.foo);
Because then you know that foo is part of the received json, you'll probably have something like:
let key = getKeySomehow();
console.log(myInstance[key]);
And this should work without an error from the compiler, the only problem with that is that the compiler doesn't know the type for the returned value, and it will be any.
So you can do this:
const myInstance = new MyClass(someJson) as MyClass & { [key: string]: string };
let foo = myInstance["foo"]; // type of foo is string
let someProperty = myInstance["someProperty"]; // type of someProperty is boolean
2nd edit
As you do know the props, but not in the class, you can do:
type ExtendedProperties<T> = { [P in keyof T]: T[P] };
function MyClassFactory<T>(json: string): MyClass & ExtendedProperties<T> {
return new MyClass(json) as MyClass & ExtendedProperties<T>;
}
Then you simply use it like so:
type Json = {
foo: string;
bar: string;
};
const myInstance = MyClassFactory<Json>(someJson);
Note that this will work only on typescript 2.1 and above.
If you want to dynamically add class properties via an object upon instantiation, and type information is available for that object, you can very nicely get full type safety in this way (as long as you don't mind using a static factory method):
class Augmentable {
constructor(augment: any = {}) {
Object.assign(this, augment)
}
static create<T extends typeof Augmentable, U>(this: T, augment?: U) {
return new this(augment) as InstanceType<T> & U
}
}
This is using the (fake) this parameter to infer the constructor type of the class. It then constructs the instance, and casts it to a union of the instance type (using the InstanceType utility type) and the inferred type of the props you passed to the method.
(We could have casted directly to Augmentable & U, however this way allows us to extend the class.)
Examples
Augment basic properties:
const hasIdProp = Augmentable.create({ id: 123 })
hasIdProp.id // number
Augment with methods:
const withAddedMethod = Augmentable.create({
sayHello() {
return 'Hello World!'
}
})
withAddedMethod.sayHello() // Properly typed, with signature and return value
Extend and augment, with this access in method augments:
class Bob extends Augmentable {
name = 'Bob'
override = 'Set from class definition'
checkOverrideFromDefinition() {
return this.override
}
}
interface BobAugment {
whatToSay: string
override: string
sayHelloTo(to: string): void
checkOverrideFromAugment(): string
}
const bobAugment: BobAugment = {
whatToSay: 'hello',
override: 'Set from augment'
sayHelloTo(this: Bob & BobAugment, to: string) {
// Let's combine a class parameter, augment parameter, and a function parameter!
return `${this.name} says '${this.whatToSay}' to ${to}!`
},
checkOverrideFromAugment(this: Bob & BobAugment) {
return this.override
}
}
const bob = Bob.create(bobAugment) // Typed as Bob & BobAugment
bob.sayHelloTo('Alice') // "Bob says 'hello' to Alice!"
// Since extended class constructors always run after parent constructors,
// you cannot override a class-set parameter with an augment, no matter
// from where you are checking it.
bob.checkOverrideFromAugment() // "Set from class definition"
bob.checkOverrideFromDefinition() // "Set from class definition"
Limitations
Augmented properties aren't really part of the class, so you can't extend a class with those augments included. This may be a feature for some use cases where the augments are temporary additions that aren't meant to modify the prototype hierarchy
It is also not easy to add non-augment arguments to .create(), however an easy work-around is to simply utilize the augment functionality to accomplish the same thing you would have with an extra argument.
You can add index signature to your class:
class MyClass {
[index: string]: any; //index signature
someProperty:boolean
constructor( json:string ) {
const parsedJson:any = JSON.parse( json )
Object.keys( parsedJson ).forEach(
( key:string ) => {
this[ key ] = parsedJson[ key ]
}
)
this['someProperty'] = true
}
}
I create a class User, and I want to create an optional out of it, compiler then fires an error
class User {
var firstName: String = ""
var lastName: String = ""
}
var Tom = User?(firstName: "Tom", lastName: "Soya")
error: cannot invoke initializer for type 'User?' with an argument list of type '(firstName: String, lastName: String)'
Question: What's wrong with it? Do I need to put more stuff inside class before I can create an optional value? If so what is it?
Thanks
The problem is that your User class has no initializers. Thus, there is only one way to initialize it: namely, by saying User(). So if you are going to define User like this:
class User {
var firstName: String = ""
var lastName: String = ""
}
Then the best you can do is this:
var tom : User? = User()
tom?.firstName = "Tom"
tom?.lastName = "Soya"
#matt's answer is correct, but here's another way, which I think is clearer:
var tom = Optional(User())
See Optional.init(_:).