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44 lines
1.6 KiB
44 lines
1.6 KiB
Command gencodec generates marshaling methods for struct types.
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When gencodec is invoked on a directory and type name, it creates a Go source file
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containing JSON and YAML marshaling methods for the type. The generated methods add
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features which the standard json package cannot offer.
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gencodec -dir . -type MyType -out mytype_json.go
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### Struct Tags
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All fields are required unless the "optional" struct tag is present. The generated
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unmarshaling method returns an error if a required field is missing. Other struct tags are
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carried over as is. The standard "json" and "yaml" tags can be used to rename a field when
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marshaling.
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Example:
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type foo struct {
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Required string
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Optional string `optional:""`
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Renamed string `json:"otherName"`
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}
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### Field Type Overrides
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An invocation of gencodec can specify an additional 'field override' struct from which
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marshaling type replacements are taken. If the override struct contains a field whose name
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matches the original type, the generated marshaling methods will use the overridden type
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and convert to and from the original field type.
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In this example, the specialString type implements json.Unmarshaler to enforce additional
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parsing rules. When json.Unmarshal is used with type foo, the specialString unmarshaler
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will be used to parse the value of SpecialField.
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//go:generate gencodec -dir . -type foo -field-override fooMarshaling -out foo_json.go
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type foo struct {
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Field string
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SpecialField string
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}
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type fooMarshaling struct {
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SpecialField specialString // overrides type of SpecialField when marshaling/unmarshaling
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}
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