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Covariance and contravariance real world example
I'm having a little trouble understanding how I would use covariance and contravariance in the real world.
9 Answers
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`levels
...are good, but they are missing an important point. Let me try and describe it.
R is a functional language and does not like to mutate its objects. But it does allow assignment statements, using replacement functions:
levels(x) <- y
is equivalent to
x <- `levels<-`(x, y)
The trick is,...
What's the difference between Task.Start/Wait and Async/Await?
...sing something
You are.
what is the difference between doing Task.Wait and await task?
You order your lunch from the waiter at the restaurant. A moment after giving your order, a friend walks in and sits down next to you and starts a conversation. Now you have two choices. You can ignore yo...
C default arguments
...
Not really. The only way would be to write a varargs function and manually fill in default values for arguments which the caller doesn't pass.
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How to skip “Loose Object” popup when running 'git gui'
When I run 'git gui' I get a popup that says
4 Answers
4
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How can I override Bootstrap CSS styles?
I need to modify bootstrap.css to fit my website. I feel it's better to create a separate custom.css file instead of modifying bootstrap.css directly, one reason being that should bootstrap.css get an update, I'll suffer trying to re-include all my modifications. I'll sacrifice some load tim...
Converting a view to Bitmap without displaying it in Android?
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there is a way to do this. you have to create a Bitmap and a Canvas and call view.draw(canvas);
here is the code:
public static Bitmap loadBitmapFromView(View v) {
Bitmap b = Bitmap.createBitmap( v.getLayoutParams().width, v.getLayoutParams().height, Bitmap.Config.ARG...
How does python numpy.where() work?
I am playing with numpy and digging through documentation and I have come across some magic. Namely I am talking about numpy.where() :
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Give examples of functions which demonstrate covariance and contravariance in the cases of both over
...per {
String getSomething() {}
}
Sub#getSomething is covariant because it returns a subclass of the return type of Super#getSomething (but fullfills the contract of Super.getSomething())
Contravariance
class Super{
void doSomething(String parameter)
}
class Sub extends Super{
void doSometh...
Reverse a string in Python
...gt;> 'hello world'[::-1]
'dlrow olleh'
This is extended slice syntax. It works by doing [begin:end:step] - by leaving begin and end off and specifying a step of -1, it reverses a string.
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