mirror of https://github.com/dmarkham/enumer.git
148 lines
6.0 KiB
Markdown
148 lines
6.0 KiB
Markdown
# Enumer [](https://godoc.org/github.com/alvaroloes/enumer) [](https://goreportcard.com/report/github.com/alvaroloes/enumer) [](https://cover.run/go/github.com/alvaroloes/enumer?tag=golang-1.10)
|
||
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).
|
||
|
||
# Install
|
||
|
||
```
|
||
go get github.com/alvaroloes/enumer
|
||
```
|
||
|
||
## 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 `<Type>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.
|
||
* Function `<Type>Values()`: returns a slice with all the values of the enum
|
||
* Method `IsA<Type>()`: 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 will be also generated.
|
||
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 (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")
|
||
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 snake_case or kebab-case, 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 form CamelCase to snake_case or kebab-case, not the other way around.
|
||
|
||
## How to use
|
||
The usage of Enumer is the same as Stringer, so you can refer to the [Stringer docs](https://godoc.org/golang.org/x/tools/cmd/stringer)
|
||
for more information.
|
||
|
||
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 `snake` and `kebab` for transformation to snake_case and kebab-case accordingly.
|
||
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). If a name doesn't have the prefix it will be passed unchanged.
|
||
|
||
## Inspiring projects
|
||
* [Stringer](https://godoc.org/golang.org/x/tools/cmd/stringer)
|
||
* [jsonenums](https://github.com/campoy/jsonenums)
|