encoding/json/v2: reduce allocations when checking IsZero by philpearl · Pull Request #80879 · golang/go

philpearl · 2026-08-14T09:41:12Z

When checking whether an omitzero field is zero via an IsZero method,
calling Interface() on a value type causes a heap allocation due to
interface boxing.

Reorder the switch cases to check if reflect.PointerTo(sf.Type)
implements the isZeroer interface before checking sf.Type directly.
Because pointer method sets include value methods, this allows using
va.Addr().Interface(), which avoids boxing value types and eliminates
the extra allocation per field.

Fixes #80868

… omitzero field implements IsZero Where I work we have structs with many small fields with IsZero methods. Marshalling these structs with json/v2 causes many allocations, one per such field. I tracked the allocation down to the code that checks for and calls the IsZero method. Calling reflect.Value.Interface{} causes an allocation when the value is not a pointer type. Removing the excess allocation is as easy as switching the order of two lines in a switch statement so that the case that tries to use a pointer to the field is tried first. Before: BenchmarkMarshal/OmitZeroMethod-10 14441822 83.81 ns/op 23.86 MB/s 16 B/op 2 allocs/op After BenchmarkMarshal/OmitZeroMethod-10 14114629 80.38 ns/op 24.88 MB/s 8 B/op 1 allocs/op Fixes golang#80868 Change-Id: I3c1da4946e16a94e70658cdfa02e2b5e29b5c6a5

gopherbot · 2026-08-14T10:06:42Z

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gopherbot · 2026-08-14T10:24:57Z

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gopherbot · 2026-08-14T10:24:58Z

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gopherbot · 2026-08-14T11:43:19Z

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Patch Set 2:

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gopherbot · 2026-08-14T11:43:20Z

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gopherbot · 2026-08-14T12:03:04Z

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gopherbot · 2026-08-14T15:15:36Z

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Patch Set 3: Commit-Queue+1

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gopherbot · 2026-08-14T15:15:37Z

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gopherbot · 2026-08-14T16:29:03Z

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gopherbot · 2026-08-14T16:29:03Z

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gopherbot · 2026-08-14T17:07:09Z

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philpearl · 2026-08-14T17:28:46Z

Removed this from the PR description in an attempt to fix some Gerrit stuff that I don't understand

Change-Id: I3c1da4946e16a94e70658cdfa02e2b5e29b5c6a5

philpearl · 2026-08-14T17:31:22Z

Does kicking this again do anything?

philpearl · 2026-08-14T17:35:38Z

Come on gerrit bot. Do something!

gopherbot · 2026-08-14T17:42:32Z

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gopherbot · 2026-08-14T18:01:40Z

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Patch Set 5:

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gopherbot · 2026-08-14T18:39:43Z

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gopherbot · 2026-08-14T18:39:44Z

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philpearl changed the title ~~encoding/json/v2: reduce marshal allocs when an omitzero field has IsZero~~ encoding/json/v2: reduce allocations when checking IsZero Aug 14, 2026

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philpearl commented Aug 14, 2026 •

edited by thepudds

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