can somebody help
I am working in C# and I want to use ? : operator.
I do not need get solution status I only need play different sound for flushing/noFlushing button
My code is
var status = lSBControl.FlashConfirmButtonOnShowContentTab ? (override)
ExecutiveControl.Instance.IVDStateModel.TheIVDInterface.PlaySound(PA.HomeHelp.IVDGlobal.SystemSounds.ButtonClick)
ExecutiveControl.Instance.IVDStateModel.TheIVDInterface.PlaySound(PA.HomeHelp.IVDGlobal.SystemSounds.ButtonNoClick);
:
The conditional operator can only be used with expressions that have values (of compatible types).
You need to use if/else.
Related
The following works in Flutter, however, I have an IDE warning to avoid "unnecessary statements." I'm sure many will pipe in citing the Latin root of three in ternary and other critiques, and I appreciate that kind of fun dialog, I really do, however, sometimes in a nested sequence, this stuff comes up..not just in the simple example I'm giving.
As I said, the below works, I just get an Android Studio IDE warning. I'd probably be better off to correct it if there is something more appropriate when using a ternary operator
x == 4 ? doSomething() : null
Couldn't find any documentation on this.
Just don't use ternary.
if( x == 4 ) doSomething()
Applies to List and Map as well.
Android Studio at least has updated this check and it is now allowed without warnings. It was a common logic in validators at least, and someone saw the light. So the correct answer was: It's perfectly reasonable and good code. (at least in my opinion!)
The ternary operator is not built for such a situation. It should use where we have at least two options
condition ? doThisIfTrue() : doThisIfFalse()
If we have only one option, then simply use if
if ( condition ) {
doThis
}
The code that you wrote, is not wrong either, but that is not use of ternary operator.
I can see that Subject.eraseToAnySubject() returns the concrete Subject type AnySubject. I'm assuming this is using a type eraser pattern.
However, the apple docs provide almost no details: https://developer.apple.com/documentation/combine/passthroughsubject/3241547-erasetoanysubject
Can anyone explain how this works and where it should be used?
Also, would it be possible to use the some keyword to avoid using AnySubject?
In Combine, as you chain Publishers to Operators, the return type becomes complicated very quickly since it includes specific detail about each publisher in the chain.
For example a simple string Publisher with a filter and map Operator attached will have a return type of: <Filter<Map<Published<String, Error>>>>
eraseToAny uses a type eraser pattern to capture what's actually important about the return type. In the example given, adding an eraseToAnyPublisher will shorten the type to a more succinct <AnyPublisher<String, Error>>
My codes looks like this:
_user.role >= level if _user?
I tried the codes below, but found it didn't work
_user?.role >= level
Does anyone have ideas about write shorter codes for this?
What do you want in case _user is null? If you want nothing (undefined), then use the first code. If you want false, then use second one. Or want another value from the expression?
I created a sample project and a framework next to it. The framework is called "SampleFramework". Then I created a custom operator in SampleFramework. Here is what it looks like:
infix operator >>= {associativity left}
public func >>=<A, B>(a: A?, f: A -> B?) -> B? {
if let a = a { return f(a) }
else { return .None }
}
Then I wanted to use it my main application. I imported the SampleFramework to my source file and then I wrote this code to test it:
NSURL(string: "www.google.com") >>= { println("\($0)") }
It didn't compile. Here is Xcode's error message:
Ambiguous operator declarations found for operator. Operator is not a
known binary operator
I can confirm that that what you are seeing is what really happens. I just tried it myself and I've seen the same result.
My opinion is that >>= is somehow conflicting with some other operator (probably the bite shift operator: >>) or is being declared somewhere else too (you can see why I think that here). I did successfully declared custom operators in a framework and used those in the main app code before (you can see that here for example).
What I would suggest is rename your custom operator to something else. When I did that (renamed the custom operator to >>>=) the compiler stopped complaining and my app compiled just fine.
Later edit
Ok. So this might help a bit more. Basically when an operator is already declared and you want to add extra functionality to that operator (for example doing things like 3 * "Hello" like Johan Kool said he wanted to) all you have to do is overload that operator's method.
Basically, in your specific case I am now 100% that >>= is an already declared operator and you can go ahead and just add these lines in your framework:
public func >>=<A, B>(a: A?, f: A -> B?) -> B? {
if let a = a { return f(a) }
else { return .None }
}
This will make your operator work. BUT it will inherit the precedence and associativity of the original operator thus giving you less control over how it's supposed to behave.
I figured it out. I think declaration of operator (infix operator >>= {associativity left}) is module specific. You can't apply access control to it. But the operator function can be accessed in other modules. So in order to make this work I had to copy operator declaration and paste it to main project.
It seems to be sufficient to just add the
infix operator + : Additive
in each source where you want to apply your framework-defined operator, assuming that your framework has some
public func + (lhs: ...
declared.
Anyhow, it's nasty to have the need for adding this if you use a framework and I'd like to see some way to have some global approach where importing a framework also makes available the operators automatically.
Edit After fiddling around for hours, the problem went away. I have not figured out what's the cause. I had lots of infix declarations in my basic framework (for historic reason). Once I got rid of them, everything went to normal. So now that I have only infix for the new operators, it's fine. But obviously re-declaring existing ones (like *, +, etc.) Swift seems to get hick-ups.
Let's say I get two instances in my code and I don't know their types. How to check it?
If in Java, I can use this code:
a.getClass() == b.getClass()
But in Dart, I can't find similar methods. Although there is the dart:mirrors providing reflect(instance) function, which may let me do it, but I'm not sure if that's a correct solution since it looks complicated.
a.runtimeType == b.runtimeType
I think dart:mirrors (reflection) API helps you. Look at this page :
http://blog.dartwatch.com/2012/06/dartmirrors-reflection-api-is-on-way.html
Also you can look this question(with runtime solution)
How do I get the qualified name from a Type instance, in Dart?
if you want to compare a and b you can use
if(a.runtimeType == b.runtimeType);
but if you want to confirm that a is the type you want you need to do this
if(a.runtimeType.toString()=="DivElement");//a is a div for instance
because runtimeType's value is not a string