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https://github.com/dmarkham/enumer

A Go tool to auto generate methods for your enums
https://github.com/dmarkham/enumer

code-generation codegeneration codegenerator enum enums generator golang

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A Go tool to auto generate methods for your enums

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# Enumer [![GoDoc](https://godoc.org/github.com/dmarkham/enumer?status.svg)](https://godoc.org/github.com/dmarkham/enumer) [![Go Report Card](https://goreportcard.com/badge/github.com/dmarkham/enumer)](https://goreportcard.com/report/github.com/dmarkham/enumer) [![GitHub Release](https://img.shields.io/github/release/dmarkham/enumer.svg)](https://github.com/dmarkham/enumer/releases)



Enumer is a tool to generate Go code that adds useful methods to Go enums (constants with a specific type).

It started as a fork of [Rob Pike’s Stringer tool](https://godoc.org/golang.org/x/tools/cmd/stringer)

maintained by [Álvaro López Espinosa](https://github.com/alvaroloes/enumer). 

This was again forked here as (https://github.com/dmarkham/enumer) picking up where Álvaro left off.



```

$ enumer --help

Enumer is a tool to generate Go code that adds useful methods to Go enums (constants with a specific type).

Usage of enumer:

        Enumer [flags] -type T [directory]

        Enumer [flags] -type T files... # Must be a single package

For more information, see:

        http://godoc.org/github.com/dmarkham/enumer

Flags:

  -addprefix string

        transform each item name by adding a prefix. Default: ""

  -comment value

        comments to include in generated code, can repeat. Default: ""

  -gqlgen

        if true, GraphQL marshaling methods for gqlgen will be generated. Default: false

  -json

        if true, json marshaling methods will be generated. Default: false

  -linecomment

        use line comment text as printed text when present

  -output string

        output file name; default srcdir/_string.go

  -sql

        if true, the Scanner and Valuer interface will be implemented.

  -text

        if true, text marshaling methods will be generated. Default: false

  -transform string

        enum item name transformation method. Default: noop (default "noop")

  -trimprefix string

        transform each item name by removing a prefix or comma separated list of prefixes. Default: ""

  -type string

        comma-separated list of type names; must be set

  -values

        if true, alternative string values method will be generated. Default: false

  -yaml

        if true, yaml marshaling methods will be generated. Default: false

```



## Generated functions and methods



When Enumer is applied to a type, it will generate:



- The following basic methods/functions:



  - Method `String()`: returns the string representation of the enum value. This makes the enum conform

    the `Stringer` interface, so whenever you print an enum value, you'll get the string name instead of a number.

  - Function `String(s string)`: returns the enum value from its string representation. This is useful

    when you need to read enum values from command line arguments, from a configuration file, or

    from a REST API request... In short, from those places where using the real enum value (an integer) would

    be almost meaningless or hard to trace or use by a human. `s` string is Case Insensitive.

  - Function `Values()`: returns a slice with all the values of the enum

  - Function `Strings()`: returns a slice with all the Strings of the enum

  - Method `IsA()`: returns true only if the current value is among the values of the enum. Useful for validations.



- When the flag `json` is provided, two additional methods will be generated, `MarshalJSON()` and `UnmarshalJSON()`. These make

  the enum conform to the `json.Marshaler` and `json.Unmarshaler` interfaces. Very useful to use it in JSON APIs.

- When the flag `text` is provided, two additional methods will be generated, `MarshalText()` and `UnmarshalText()`. These make

  the enum conform to the `encoding.TextMarshaler` and `encoding.TextUnmarshaler` interfaces.

  **Note:** If you use your enum values as keys in a map and you encode the map as _JSON_, you need this flag set to true to properly

  convert the map keys to json (strings). If not, the numeric values will be used instead

- When the flag `yaml` is provided, two additional methods will be generated, `MarshalYAML()` and `UnmarshalYAML()`. These make

  the enum conform to the `gopkg.in/yaml.v2.Marshaler` and `gopkg.in/yaml.v2.Unmarshaler` interfaces.

- When the flag `sql` is provided, the methods for implementing the `Scanner` and `Valuer` interfaces.

  Useful when storing the enum in a database.



For example, if we have an enum type called `Pill`,



```go

type Pill int



const (

	Placebo Pill = iota

	Aspirin

	Ibuprofen

	Paracetamol

	Acetaminophen = Paracetamol

)

```



executing `enumer -type=Pill -json` will generate a new file with four basic methods and two extra for JSON:



```go

func (i Pill) String() string {

	//...

}



func PillString(s string) (Pill, error) {

	//...

}



func PillValues() []Pill {

	//...

}



func PillStrings() []string {

	//...

}



func (i Pill) IsAPill() bool {

	//...

}



func (i Pill) MarshalJSON() ([]byte, error) {

	//...

}



func (i *Pill) UnmarshalJSON(data []byte) error {

	//...

}

```



From now on, we can:



```go

// Convert any Pill value to string

var aspirinString string = Aspirin.String()

// (or use it in any place where a Stringer is accepted)

fmt.Println("I need ", Paracetamol) // Will print "I need Paracetamol"



// Convert a string with the enum name to the corresponding enum value

pill, err := PillString("Ibuprofen") // "ibuprofen" will also work.

if err != nil {

    fmt.Println("Unrecognized pill: ", err)

    return

}

// Now pill == Ibuprofen



// Get all the values of the string

allPills := PillValues()

fmt.Println(allPills) // Will print [Placebo Aspirin Ibuprofen Paracetamol]



// Check if a value belongs to the Pill enum values

var notAPill Pill = 42

if (notAPill.IsAPill()) {

	fmt.Println(notAPill, "is not a value of the Pill enum")

}



// Marshal/unmarshal to/from json strings, either directly or automatically when

// the enum is a field of a struct

pillJSON := Aspirin.MarshalJSON()

// Now pillJSON == `"Aspirin"`

```



The generated code is exactly the same as the Stringer tool plus the mentioned additions, so you can use

**Enumer** where you are already using **Stringer** without any code change.



## Transforming the string representation of the enum value



By default, Enumer uses the same name of the enum value for generating the string representation (usually CamelCase in Go).



```go

type MyType int



 ...



name := MyTypeValue.String() // name => "MyTypeValue"

```



Sometimes you need to use some other string representation format than CamelCase (i.e. in JSON).



To transform it from CamelCase to another format, you can use the `transform` flag.



For example, the command `enumer -type=MyType -json -transform=snake` would generate the following string representation:



```go

name := MyTypeValue.String() // name => "my_type_value"

```



**Note**: The transformation only works from CamelCase to snake_case or kebab-case, not the other way around.



### Transformers



- snake

- snake-upper

- kebab

- kebab-upper

- lower (lowercase)

- upper (UPPERCASE)

- title (TitleCase)

- title-lower (titleCase)

- first (Use first character of string)

- first-lower (same as first only lower case)

- first-upper (same as first only upper case)

- whitespace



## How to use



For a module-aware repo with `enumer` in the `go.mod` file, generation can be called by adding the following to a `.go` source file:



```golang

//go:generate go run github.com/dmarkham/enumer -type=YOURTYPE

```



There are four boolean flags: `json`, `text`, `yaml` and `sql`. You can use any combination of them (i.e. `enumer -type=Pill -json -text`),



For enum string representation transformation the `transform` and `trimprefix` flags

were added (i.e. `enumer -type=MyType -json -transform=snake`).

Possible transform values are listed above in the [transformers](#transformers) section.

The default value for `transform` flag is `noop` which means no transformation will be performed.



If a prefix is provided via the `trimprefix` flag, it will be trimmed from the start of each name (before

it is transformed). You can trim multiple prefixes by passing a comma separated list.

If a name doesn't have the prefix it will be passed unchanged.



If a prefix is provided via the `addprefix` flag, it will be added to the start of each name (after trimming and after transforming).



The boolean flag `values` will additionally create an alternative string values method `Values() []string` to fullfill the `EnumValues` interface of [ent](https://entgo.io/docs/schema-fields/#enum-fields).



## Inspiring projects



- [Álvaro López Espinosa](https://github.com/alvaroloes/enumer)

- [Stringer](https://godoc.org/golang.org/x/tools/cmd/stringer)

- [jsonenums](https://github.com/campoy/jsonenums)