jsonenums/README.md

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.