Hi Developers from GDG Shanghai I d like ask why simplest co kotlinlang #compose

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Hi Developers, from GDG Shanghai. I'd like ask why...

# compose

Alimjan Qadir

08/10/2023, 12:32 PM

Hi Developers, from GDG Shanghai. I'd like ask why simplest component like Spacer still creates 3 Replaceable Group?

Alimjan Qadir

08/10/2023, 1:21 PM

image.png

thank you color 2

Alimjan Qadir

08/10/2023, 1:22 PM

I can't see any flow control in the source code

Alimjan Qadir

08/10/2023, 1:22 PM

Code shrinking won't remove those calls either, what I'm missing?

Alimjan Qadir

08/10/2023, 1:22 PM

image.png

Alimjan Qadir

08/10/2023, 1:23 PM

Why start a replaceable group record nothing and end the group?

Alimjan Qadir

08/10/2023, 1:23 PM

image.png

Alimjan Qadir

08/10/2023, 2:27 PM

I have some idea, first replaceable group is for Measurement, second is for composition local, third one is for content composable lambda, because spacer doesn't contain content third group is empty.

Alimjan Qadir

08/10/2023, 2:29 PM

I don't know whether these assumptions are true, I hope somebody could help me to confirm

shikasd

08/10/2023, 5:54 PM

you can check the groups by using sourceinformation attached to them In your example there's one for

Spacer

, one for

Layout

and one for

ReusableComposeNode

(probably)

shikasd

08/10/2023, 5:55 PM

We are working on reducing this number atm, as most of them not really required

👍 1

shikasd

08/10/2023, 5:56 PM

Could you also share more context about the empty group from the last picture, that doesn't look right

Alimjan Qadir

08/10/2023, 7:33 PM

Thanks for your response Andrei:😊

Alimjan Qadir

08/10/2023, 7:34 PM

Copy code

package androidx.compose.foundation.layout;

import androidx.compose.runtime.Applier;
import androidx.compose.runtime.ComposablesKt;
import androidx.compose.runtime.Composer;
import androidx.compose.runtime.ComposerKt;
import androidx.compose.runtime.SkippableUpdater;
import androidx.compose.runtime.Updater;
import androidx.compose.ui.Modifier;
import androidx.compose.ui.layout.LayoutKt;
import androidx.compose.ui.node.ComposeUiNode;
import androidx.compose.ui.platform.CompositionLocalsKt;
import androidx.compose.ui.platform.ViewConfiguration;
import androidx.compose.ui.unit.Density;
import androidx.compose.ui.unit.LayoutDirection;
import kotlin.Metadata;
import kotlin.jvm.functions.Function0;
import kotlin.jvm.functions.Function3;
import kotlin.jvm.internal.Intrinsics;
/* compiled from: Spacer.kt */
@Metadata(d1 = {"\u0000\u0010\n\u0000\n\u0002\u0010\u0002\n\u0000\n\u0002\u0018\u0002\n\u0002\b\u0002\u001a\u0015\u0010\u0000\u001a\u00020\u00012\u0006\u0010\u0002\u001a\u00020\u0003H\u0007¢\u0006\u0002\u0010\u0004¨\u0006\u0005"}, d2 = {"Spacer", "", "modifier", "Landroidx/compose/ui/Modifier;", "(Landroidx/compose/ui/Modifier;Landroidx/compose/runtime/Composer;I)V", "foundation-layout_release"}, k = 2, mv = {1, 8, 0}, xi = 48)
/* loaded from: /Users/alimjan/Developer/Mobile/Android/JetFocus/app/build/outputs/apk/debug/classes.dex */
public final class SpacerKt {
    public static final void Spacer(Modifier modifier, Composer $composer, int $changed) {
        Intrinsics.checkNotNullParameter(modifier, "modifier");
        $composer.startReplaceableGroup(-72882467);
        ComposerKt.sourceInformation($composer, "C(Spacer)39@1433L68:Spacer.kt#2w3rfo");
        if (ComposerKt.isTraceInProgress()) {
            ComposerKt.traceEventStart(-72882467, $changed, -1, "androidx.compose.foundation.layout.Spacer (Spacer.kt:38)");
        }
        SpacerMeasurePolicy spacerMeasurePolicy = SpacerMeasurePolicy.INSTANCE;
        int $changed$iv = (($changed << 3) & 112) | 384;
        $composer.startReplaceableGroup(-1323940314);
        ComposerKt.sourceInformation($composer, "C(Layout)P(!1,2)74@2915L7,75@2970L7,76@3029L7,77@3041L460:Layout.kt#80mrfh");
        ComposerKt.sourceInformationMarkerStart($composer, 2023513938, "C:CompositionLocal.kt#9igjgp");
        Object consume = $composer.consume(CompositionLocalsKt.getLocalDensity());
        ComposerKt.sourceInformationMarkerEnd($composer);
        Density density$iv = (Density) consume;
        ComposerKt.sourceInformationMarkerStart($composer, 2023513938, "C:CompositionLocal.kt#9igjgp");
        Object consume2 = $composer.consume(CompositionLocalsKt.getLocalLayoutDirection());
        ComposerKt.sourceInformationMarkerEnd($composer);
        LayoutDirection layoutDirection$iv = (LayoutDirection) consume2;
        ComposerKt.sourceInformationMarkerStart($composer, 2023513938, "C:CompositionLocal.kt#9igjgp");
        Object consume3 = $composer.consume(CompositionLocalsKt.getLocalViewConfiguration());
        ComposerKt.sourceInformationMarkerEnd($composer);
        ViewConfiguration viewConfiguration$iv = (ViewConfiguration) consume3;
        Function0 factory$iv$iv = ComposeUiNode.Companion.getConstructor();
        Function3 skippableUpdate$iv$iv = LayoutKt.materializerOf(modifier);
        int $changed$iv$iv = (($changed$iv << 9) & 7168) | 6;
        if (!($composer.getApplier() instanceof Applier)) {
            ComposablesKt.invalidApplier();
        }
        $composer.startReusableNode();
        if ($composer.getInserting()) {
            $composer.createNode(factory$iv$iv);
        } else {
            $composer.useNode();
        }
        $composer.disableReusing();
        Composer $this$Layout_u24lambda_u2d0$iv = Updater.m2858constructorimpl($composer);
        Updater.m2865setimpl($this$Layout_u24lambda_u2d0$iv, spacerMeasurePolicy, ComposeUiNode.Companion.getSetMeasurePolicy());
        Updater.m2865setimpl($this$Layout_u24lambda_u2d0$iv, density$iv, ComposeUiNode.Companion.getSetDensity());
        Updater.m2865setimpl($this$Layout_u24lambda_u2d0$iv, layoutDirection$iv, ComposeUiNode.Companion.getSetLayoutDirection());
        Updater.m2865setimpl($this$Layout_u24lambda_u2d0$iv, viewConfiguration$iv, ComposeUiNode.Companion.getSetViewConfiguration());
        $composer.enableReusing();
        skippableUpdate$iv$iv.invoke(SkippableUpdater.m2846boximpl(SkippableUpdater.m2847constructorimpl($composer)), $composer, Integer.valueOf(($changed$iv$iv >> 3) & 112));
        $composer.startReplaceableGroup(2058660585);
        int i = ($changed$iv$iv >> 9) & 14;
        ComposerKt.sourceInformationMarkerStart($composer, 348366764, "C:Spacer.kt#2w3rfo");
        ComposerKt.sourceInformationMarkerEnd($composer);
        $composer.endReplaceableGroup();
        $composer.endNode();
        $composer.endReplaceableGroup();
        if (ComposerKt.isTraceInProgress()) {
            ComposerKt.traceEventEnd();
        }
        $composer.endReplaceableGroup();
    }
}

Alimjan Qadir

08/10/2023, 7:36 PM

the third replaceable group become like this after shrinking

Alimjan Qadir

08/10/2023, 7:38 PM

just after updating the modifiers

Alimjan Qadir

08/10/2023, 7:53 PM

@shikasd I really couldn't get the logic behind the replaceable group, I simply thought it's about control flow, or marker for nodes, but some uses really confused me. what's the right mental model to understand the replaceable group?

shikasd

08/10/2023, 8:19 PM

The replaceable groups are currently applied to the body of every non- restartable function, including inline ones

shikasd

08/11/2023, 2:42 AM

It's caused by this line: https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:compose/runtime/runtime/src/commonMain/kotlin/androidx/compose/runtime/Composables.kt;l=333 Seems like empty composable lambda creates a group

shikasd

08/11/2023, 2:42 AM

At any rate, this is being worked on right now 🙂

Alimjan Qadir

08/11/2023, 4:00 AM

Thanks @shikasd, this clears a lot.

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