Implementing `switch` expressions [refactoring `flutter/lib/src/`] #143496

nate-thegrate · 2024-02-14T22:59:36Z

This PR is the 8ᵗʰ step in the journey to solve issue #136139 and make the entire Flutter repo more readable.

(previous pull requests: #139048, #139882, #141591, #142279, #142634, #142793, #143293)

I did a pass through all of packages/flutter/lib/src/ and found a whole bunch of switch statements to improve: most of them were really simple, but many involved some thorough refactoring.

This pull request is just the complicated stuff. 😎 I'll make comments to describe the changes, and then in the future there will be another PR (and it'll be much easier to review than this one).

Pre-launch Checklist

I read the Contributor Guide and followed the process outlined there for submitting PRs.
I read the Tree Hygiene wiki page, which explains my responsibilities.
I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
I signed the CLA.
I listed at least one issue that this PR fixes in the description above.
I updated/added relevant documentation (doc comments with ///).
I added new tests to check the change I am making, or this PR is test-exempt.
All existing and new tests are passing.

packages/flutter/lib/src/cupertino/colors.dart

nate-thegrate · 2024-02-15T01:41:54Z

packages/flutter/lib/src/material/chip.dart

      switch (textDirection!) {
        case TextDirection.rtl:
-          return Offset(x - boxSize.width, (sizes.content - boxSize.height + sizes.densityAdjustment.dy) / 2.0);
+          x -= boxSize.width;
        case TextDirection.ltr:
-          return Offset(x, (sizes.content - boxSize.height + sizes.densityAdjustment.dy) / 2.0);
+          break;
      }
+      return Offset(x, (sizes.content - boxSize.height + sizes.densityAdjustment.dy) / 2.0);


I didn't implement a switch expression here, but I did notice that the only difference between the two Offsets was that the rtl has a - boxSize.width. The way it's formatted now hopefully makes that easier to see.

packages/flutter/lib/src/material/drawer.dart

packages/flutter/lib/src/material/list_tile.dart

nate-thegrate · 2024-02-15T01:55:38Z

packages/flutter/lib/src/rendering/sliver.dart

-    bool rightWayUp;
-    switch (constraints.axisDirection) {
-      case AxisDirection.up:
-      case AxisDirection.left:
-        rightWayUp = false;
-      case AxisDirection.down:
-      case AxisDirection.right:
-        rightWayUp = true;
-    }


rightWayUp was set up to be true for AxisDirection.down & AxisDirection.right, and false otherwise.

But axisDirectionIsReversed() already does the same thing, just swapped.

nate-thegrate · 2024-02-15T02:02:41Z

packages/flutter/lib/src/rendering/viewport.dart

    assert(child.parent == this);
    assert(child is RenderSliver);
    final RenderSliver sliver = child as RenderSliver;



This code has a lot in common with the getOffsetToReveal() function that I'd refactored previously, so I made similar changes here.

nate-thegrate · 2024-02-15T02:06:39Z

packages/flutter/lib/src/services/raw_keyboard_ios.dart

+    if (modifiers & (leftMask | rightMask | anyMask) == anyMask) {
+      // If only the "anyMask" bit is set, then we respond true for requests of
+      // whether either left or right is pressed. Handles the case where iOS
+      // supplies just the "either" modifier flag, but not the left/right flag.
+      // (e.g. modifierShift but not modifierLeftShift).
+      return true;
    }


The code was originally set up as follows:

switch (side) { case KeyboardSide.any: return true; case KeyboardSide.all: return [expression] || anyOnly; case KeyboardSide.left: return [other expression] || anyOnly; case KeyboardSide.right: return [other expression] || anyOnly; }

So if anyOnly was true, the function would return true no matter what. I think it's easier to follow when the function just returns true right away instead of creating a variable.

nate-thegrate · 2024-02-15T02:54:49Z

packages/flutter/lib/src/widgets/overscroll_indicator.dart

+    final AxisDirection direction = switch (stretchDirection) {
+      _StretchDirection.trailing => widget.axisDirection,
+      _StretchDirection.leading => flipAxisDirection(widget.axisDirection),
+    };


We can avoid all those conditional expressions by just flipping the direction beforehand based on the stretchDirection.

nate-thegrate · 2024-02-15T03:01:43Z

packages/flutter/lib/src/widgets/scrollable_helpers.dart

+    if (axisDirectionToAxis(intent.direction) == axisDirectionToAxis(state.axisDirection)) {
+      final double increment = _calculateScrollIncrement(state, type: intent.type);
+      return intent.direction == state.axisDirection ? increment : -increment;
    }
+    return 0.0;


Saved the best for last! This function body has been reduced from 43 lines down to 5, and _calculateScrollIncrement() will no longer be called if it isn't needed.

flutter-dashboard · 2024-02-15T05:06:06Z

It looks like this pull request may not have tests. Please make sure to add tests before merging. If you need an exemption to this rule, contact "@test-exemption-reviewer" in the #hackers channel in Chat (don't just cc them here, they won't see it! Use Discord!).

If you are not sure if you need tests, consider this rule of thumb: the purpose of a test is to make sure someone doesn't accidentally revert the fix. Ask yourself, is there anything in your PR that you feel it is important we not accidentally revert back to how it was before your fix?

Reviewers: Read the Tree Hygiene page and make sure this patch meets those guidelines before LGTMing.

goderbauer · 2024-02-15T21:31:27Z

packages/flutter/lib/src/cupertino/colors.dart

+      (true, false, true)   => darkHighContrastColor,
+      (true, true, false)   => darkElevatedColor,
+      (true, true, true)    => darkHighContrastElevatedColor,
+    };


I find this sea of false/true makes it harder to understand what is actually going on. Is there a better way to express this that preserve a little more context of what is false/true?

I'm not a huge fan of the long CupertinoUserInterfaceLevelData name, but you have a good point that 3 bools in a row is difficult to follow. Hopefully it looks better now!

Yeah, this looks better. I wish Dart would support something similar to Swift where these could just be:

(.light, .base, false) => color,

goderbauer

LGTM

goderbauer · 2024-02-16T17:43:27Z

packages/flutter/lib/src/cupertino/colors.dart

+      (true, false, true)   => darkHighContrastColor,
+      (true, true, false)   => darkElevatedColor,
+      (true, true, true)    => darkHighContrastElevatedColor,
+    };


Yeah, this looks better. I wish Dart would support something similar to Swift where these could just be:

(.light, .base, false) => color,

loic-sharma · 2024-02-16T17:56:21Z

packages/flutter/lib/src/material/drawer.dart

-            (drawerIsStart ? padding.right : padding.left);
-      }
-    }
+    final double dragAreaWidth = widget.edgeDragWidth ?? _kEdgeDragWidth + switch ((widget.alignment, Directionality.of(context))) {


Can we break this up into multiple steps? This is a bit too busy in my opinion

Sounds good! I made whitespace changes for readability; we could break it into multiple lines (but it would no longer be final and non-nullable):

double? dragAreaWidth = widget.edgeDragWidth; dragAreaWidth ??= _kEdgeDragWidth + switch ((widget.alignment, Directionality.of(context))) { (DrawerAlignment.start, TextDirection.ltr) => MediaQuery.paddingOf(context).left, (DrawerAlignment.start, TextDirection.rtl) => MediaQuery.paddingOf(context).right, (DrawerAlignment.end, TextDirection.rtl) => MediaQuery.paddingOf(context).left, (DrawerAlignment.end, TextDirection.ltr) => MediaQuery.paddingOf(context).right, };

Gotcha. Feel free to keep it as is then :)

…rc/`] (flutter/flutter#143496)

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…143634) This PR is the 9áµ�Ê° step in the journey to solve issue #136139 and make the entire Flutter repo more readable. (previous pull requests: #139048, #139882, #141591, #142279, #142634, #142793, #143293, #143496) I did a pass through all of `packages/flutter/lib/src/` and found an abundance of `switch` statements to improve. Whereas #143496 focused on in-depth refactoring, this PR is full of simple, straightforward changes. (I ended up making some more complicated changes in `rendering/` and will file those separately after this PR is done.)

This pull request is part of the effort to solve issue #136139. The previous [`switch` expressions PR](#143496) was comprised of many simple changes throughout `flutter/lib/src/`, but due to some more in-depth refactoring in `flutter/lib/src/rendering/`, I decided to submit the changes to this directory as a separate pull request. There was really just one function that I changed significantly; I'll add a comment for explanation.

This pull request is step 12 in the journey to make this entire repository more readable. (previous PRs: #139048, #139882, #141591, #142279, #142634, #142793, #143293, #143496, #143634, #143812, #144580) We're getting close to the end! ð��

…rc/`] (flutter/flutter#143496)

nate-thegrate added 2 commits February 14, 2024 15:30

perform some really cool refactoring

8a9b365

whitespace changes

5687db5

github-actions bot added framework flutter/packages/flutter repository. See also f: labels. f: material design flutter/packages/flutter/material repository. f: scrolling Viewports, list views, slivers, etc. f: cupertino flutter/packages/flutter/cupertino repository labels Feb 14, 2024

nate-thegrate added 4 commits February 14, 2024 16:10

delete duplicate variable

19c76ed

delete old variable name

9649ba0

Merge branch 'master' into switch-expressions-8

6c19a34

remove a couple variables

70bbe4f

nate-thegrate marked this pull request as ready for review February 15, 2024 01:29

nate-thegrate commented Feb 15, 2024

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nate-thegrate changed the title ~~switch expressions, episode 8: refactoring flutter/lib/src/~~ Implementing switch expressions [refactoring flutter/lib/src/] Feb 15, 2024

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nate-thegrate added 5 commits February 15, 2024 17:15

more descriptive cupertino color switch expression

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fix spelling

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Merge branch 'master' into switch-expressions-8

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re-order declarations

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whitespace

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changes based on @loic-sharma's review

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Implementing switch expressions: everything in flutter/lib/src/ #143634

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Implementing switch expressions in rendering/ #143812

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Implementing switch expressions in flutter_tools/ #145632

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nate-thegrate added the refactor Improving readability/efficiency without behavioral changes label Jul 12, 2024

Implementing switch expressions [refactoring flutter/lib/src/] #143496

Implementing switch expressions [refactoring flutter/lib/src/] #143496

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nate-thegrate commented Feb 14, 2024

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Implementing `switch` expressions [refactoring `flutter/lib/src/`] #143496

Implementing `switch` expressions [refactoring `flutter/lib/src/`] #143496

loic-sharma Feb 16, 2024 •

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