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proposal: encoding/json: skipping nil values when Unmarshal bytes #53104

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mikolajsemeniuk opened this issue May 27, 2022 · 5 comments
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@mikolajsemeniuk
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mikolajsemeniuk commented May 27, 2022

Currently if w have struct like this:

type Product struct {
	Variants    []Variant `json:"variants"`
}

func (p *Product) Transform(input []byte) error {
	return json.Unmarshal(input, p)
}

There is no way to skip nil values so unmarshalling this json:

{
    "variants": [
         null,
        {
            "one": "two"
        },
        null,
    ]
}

Will produce:

product := Product{
	Variants: [] Variant{ 
                 {
 			One: "",
		},
	        {
 			One: "two",
		},
		{
 			One: "",
		},
	}
}

Would be nice if Unmarshal can skip nil values using something like this:

type Product struct {
	Variants    []Variant `json:"variants,skipempty"`
}

func (p *Product) Transform(input []byte) error {
	return json.Unmarshal(input, p)
}

What would product:

product := Product{
	Variants: []Variant{ 
	        {
 			One: "two",
		},
	}
}
@gopherbot gopherbot added this to the Proposal milestone May 27, 2022
@mikolajsemeniuk mikolajsemeniuk changed the title proposal: encoding/json: skipping nil values with "skip" tag when Unmarshal bytes proposal: encoding/json: skipping nil values with when Unmarshal bytes May 27, 2022
@mikolajsemeniuk mikolajsemeniuk changed the title proposal: encoding/json: skipping nil values with when Unmarshal bytes proposal: encoding/json: skipping nil values when Unmarshal bytes May 27, 2022
@ianlancetaylor
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ianlancetaylor commented May 27, 2022

Dup of #22480?

@beoran
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beoran commented May 28, 2022

@mikolajsemeniuk is the omitempty tag not what you need?

@seankhliao
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seankhliao commented May 28, 2022

This looks different, but niche:
the tag is on the slice, and it wants to skip elements inside the slice if they are null.
Both the omitempty tag and the omitnil proposal only apply if the entire slice is nil/null.

@dsnet
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dsnet commented May 29, 2022

I believe anything about omitempty is a red-herring. The OP is asking about a change to Unmarshal behavior, while omitempty and related issues are about Marshal behavior.

@mikolajsemeniuk, what is the representation of the Variant type? In order for the behavior you're asking for to make sense, there must be a representation for Variant that naturally corresponds with a JSON null.

@mikolajsemeniuk
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mikolajsemeniuk commented May 29, 2022

@dsnet this is representation of Variant:

type Variant struct {
    Name string `json:"name"`
}

@ianlancetaylor ianlancetaylor added this to Incoming in Proposals (old) Jun 8, 2022
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