jsonenums

by campoy

campoy / jsonenums

This tool is similar to golang.org/x/tools/cmd/stringer but generates MarshalJSON and UnmarshalJSON ...

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jsonenums

jsonenums is a tool to automate the creation of methods that satisfy the

json.Marshaler
and
json.Unmarshaler
interfaces. Given the name of a (signed or unsigned) integer type T that has constants defined, jsonenums will create a new self-contained Go source file implementing
func (t T) MarshalJSON() ([]byte, error)
func (t *T) UnmarshalJSON([]byte) error

The file is created in the same package and directory as the package that defines T. It has helpful defaults designed for use with go generate.

jsonenums is a simple implementation of a concept and the code might not be the most performant or beautiful to read.

For example, given this snippet,

package painkiller

type Pill int

const ( Placebo Pill = iota Aspirin Ibuprofen Paracetamol Acetaminophen = Paracetamol )

running this command

jsonenums -type=Pill

in the same directory will create the file

pill_jsonenums.go
, in package
painkiller
, containing a definition of
func (r Pill) MarshalJSON() ([]byte, error)
func (r *Pill) UnmarshalJSON([]byte) error

MarshalJSON
will translate the value of a
Pill
constant to the
[]byte
representation of the respective constant name, so that the call
json.Marshal(painkiller.Aspirin)
will return the bytes
[]byte("\"Aspirin\"")
.

UnmarshalJSON
performs the opposite operation; given the
[]byte
representation of a
Pill
constant it will change the receiver to equal the corresponding constant. So given
[]byte("\"Aspirin\"")
the receiver will change to
Aspirin
and the returned error will be
nil
.

Typically this process would be run using go generate, like this:

//go:generate jsonenums -type=Pill

If multiple constants have the same value, the lexically first matching name will be used (in the example, Acetaminophen will print as "Paracetamol").

With no arguments, it processes the package in the current directory. Otherwise, the arguments must name a single directory holding a Go package or a set of Go source files that represent a single Go package.

The

-type
flag accepts a comma-separated list of types so a single run can generate methods for multiple types. The default output file is t_jsonenums.go, where t is the lower-cased name of the first type listed. The suffix can be overridden with the
-suffix
flag and a prefix may be added with the
-prefix
flag.

This is not an official Google product (experimental or otherwise), it is just code that happens to be owned by Google.

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