Minor review suggestions #3
Open
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This is complete rewrite of the old scala.collection.immutable.Vector. The design differs from the old one in one important aspect: Instead of a single movable finger (the "display" pointers) it has a fixed finger at each end. These fingers are part of the proper data structure, not a transient optimization. There are no other ways to get to the data in the fingers (it is not part of the main data array), no focus point, and no stabilization. As a side-effect, the data structure is completely immutable and no extra memory fences are required. A second major difference lies in the implementation. Whereas the old Vector uses a single class for collections of all supported sizes, the new one is split into Vector0 to Vector6 for the different dimensions of the main data array.
szeiger
reviewed
Feb 25, 2020
|
|
||
| override final def iterator: Iterator[A] = | ||
| if(this.isInstanceOf[Vector0.type]) Vector.emptyIterator | ||
| if(this eq Vector0) Vector.emptyIterator |
There was a problem hiding this comment.
comparing the instance requires getting the instance first, a type check is faster
szeiger
reviewed
Feb 25, 2020
Comment on lines
123
to
126
| override final def length: Int = | ||
| if(this.isInstanceOf[BigVector[_]]) this.asInstanceOf[BigVector[_]].length0 | ||
| else prefix1.length | ||
| override final def length: Int = this match { | ||
| case value: BigVector[_] => value.length0 | ||
| case _ => prefix1.length | ||
| } |
There was a problem hiding this comment.
I didn't measure the impact but the pattern match creates some unnecessary bytecode instructions:
public final int length();
descriptor: ()I
Code:
0: aload_0
1: instanceof #485 // class scala/collection/immutable/BigVector
4: ifeq 15
7: aload_0
8: checkcast #485 // class scala/collection/immutable/BigVector
11: invokevirtual #488 // Method scala/collection/immutable/BigVector.length0:()I
14: ireturn
15: aload_0
16: invokevirtual #490 // Method prefix1:()[Ljava/lang/Object;
19: arraylength
20: ireturn
public final int length();
descriptor: ()I
Code:
0: aload_0
1: instanceof #490 // class scala/collection/immutable/BigVector
4: ifeq 18
7: aload_0
8: checkcast #490 // class scala/collection/immutable/BigVector
11: invokevirtual #493 // Method scala/collection/immutable/BigVector.length0:()I
14: istore_1
15: goto 24
18: aload_0
19: invokevirtual #495 // Method prefix1:()[Ljava/lang/Object;
22: arraylength
23: istore_1
24: iload_1
25: ireturn
There was a problem hiding this comment.
Hehe. Instead of just ireturning, it istore_1s, gotos, iload_1s and then ireturns.
|
hehe, bytecode shedding 🙂 just pick what seems right to you |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
No description provided.