foldLeft is a classic higher order function. Every functional programming language will have this plus multiple variants of it in their standard library. Newer non-functional programing languages will have it too. Writing implementations of foldLeft and foldRight is standard for learning recursive functions.
The lambda is applied to the initial value (0 or Map.empty[Int, Int]) and the first item in the list. The return type of the lambda must be the same type as the initial value. It then repeats the processes on the second value in the list, but using the previous result, and so on until theres no more items.
In the example above, c will change like you’d expect a mutable solution would but its a new Map each time. This might sound inefficient but its not really. Because each Map is immutable it can be optimized to share memory of the past Maps it was constructed from. Thats something you absolutely cannot do if your structures are mutable.
No. Persistent Data Structures are not mutable. The memory space of an older version is not rewritten, it is referenced by the newer version as a part of its definition. ie via composition. It can only safely do this if the data it references is guaranteed to not change.
In this example both x and y are single linked lists. y is a node with value 3 and a pointer to x. If x was mutable then changing x would change y. That’s bad™ so its not allowed.
Frankly it’s been a while since I wrote either one. I just assumed Java because of the naming convention, and I didn’t see anything I took as obviously un-Java in the class definition
Wait a minute, that’s an actual thing in java!? What the fuck Java I already didn’t like you and now you start pulling this shit? What even is the point of creating standards if you design backdoors to them
What even is the point of creating standards if you design backdoors to them
If you’re building in a backdoor anyways, why would the backdoor require 5 lines of weird reflection to get the type, type info, fieldinfo with the correct binding flags, and then invoking the method?
I think it’s kinda neat compared to C#, just being able to say “Ignore private/protected/internal keywords”
If you want to be able to eg. (de)serialize non-public fields of a type for any reason, you’ll need some way to get around the access restriction. Mocking is another use case – although it’s a philosophical discussion whether you should be mocking non-public fields.
And this isn’t just a Java thing, the comment you’re responding to has an example in C#, and you can do something similar in a lot of languages that support runtime reflection. Barring runtime reflection support you can do pointer math if the language supports it. Access restrictions on fields are there to stop casual misuse of private fields, but sometimes you actually may want to be able to step over those restrictions if you really know what you’re doing.
Reflection is sometimes a necessary evil. At least it makes it harder to abuse the class and if you do, then you are responsible if something goes wrong.
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