mirror of https://github.com/dmarkham/enumer.git
82 lines
2.9 KiB
Markdown
82 lines
2.9 KiB
Markdown
#Enumer
|
||
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).
|
||
|
||
##Generated functions and methods
|
||
When Enumer is applied to a type, it will generate three methods and one function:
|
||
|
||
* A method `String()` that 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.
|
||
* A function `<Type>String(s string)` to get the enum value from its string representation. This is useful
|
||
when you need to read enum values from the command line arguments, from a configuration file,
|
||
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.
|
||
* And two more methods, `MarshalJSON()` and `UnmarshalJSON()`, that makes the enum conform
|
||
the `json.Marshaler` and `json.Unmarshaler` interfaces. Very useful to use it in JSON APIs.
|
||
|
||
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` will generate a new file with four methods:
|
||
```go
|
||
func (i Pill) String() string {
|
||
//...
|
||
}
|
||
|
||
func PillString(s string) (Pill, error) {
|
||
//...
|
||
}
|
||
|
||
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
|
||
|
||
// 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.
|
||
|
||
## 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 two flags added: `noJSON` and `sql`. If the noJSON flag is set to true (i.e. `enumer -type=Pill -noJSON`),
|
||
the JSON related methods won't be generated. And if the sql flag is set to true, the Scanner and Valuer interface will
|
||
be implemented to seamlessly use the enum in a database model.
|
||
|
||
## Inspiring projects
|
||
* [Stringer](https://godoc.org/golang.org/x/tools/cmd/stringer)
|
||
* [jsonenums](https://github.com/campoy/jsonenums)
|