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https://github.com/meowgorithm/defaults
Enforce default values on structs in Go
https://github.com/meowgorithm/defaults
Last synced: about 2 months ago
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Enforce default values on structs in Go
- Host: GitHub
- URL: https://github.com/meowgorithm/defaults
- Owner: meowgorithm
- License: mit
- Created: 2021-10-18T15:35:24.000Z (about 3 years ago)
- Default Branch: main
- Last Pushed: 2022-08-15T18:22:12.000Z (over 2 years ago)
- Last Synced: 2024-10-16T19:19:30.129Z (2 months ago)
- Language: Go
- Size: 5.86 KB
- Stars: 28
- Watchers: 3
- Forks: 1
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
Awesome Lists containing this project
README
Defaults
========
Enforce default values on struct fields.
```go
type User struct {
Name string `default:"Goku"`
Power float64 `default:"9000.01"`
}
var u User
err := defaults.Apply(&u)
if err != nil {
log.Fatal("Uh oh: %v", err)
}
fmt.Print(u.Name) // Goku
fmt.Print(u.Power) // 9000.01
```
Defaults are only applied to fields at their zero value.
```go
type Config struct {
Host *string `default:"0.0.0.0"`
Port *int `default:"8000"`
}
var cfg Config
json.Unmarshal([]byte(`{Host: "charm.sh"}`), &cfg)
if err := defaults.Apply(&cfg); err != nil {
log.Fatal("Rats: %v", err)
}
fmt.Print(cfg.Host) // charm.sh
fmt.Print(cfg.Port) // 8000
```
Works well with JSON, Yaml, and so on.
```go
type Config struct {
Host string `json:"host" default:"0.0.0.0"`
Port int `json:"port" default:"8000"`
Debug bool `json:"debug" default:"true"`
}
```
## Supported Types
The following types are supported:
* `string`
* `bool`
* `int`
* `int8`
* `int16`
* `int32` (and `rune`, with some caveats)
* `int64`
* `uint`
* `uint8`
* `uint16`
* `uint32`
* `uint64`
* `float32`
* `float64`
* `[]byte`/`[]uint8`
…as well as pointers to those types.
### Embedded Structs
Embedded structs are supported. The following will parse as expected:
```go
type GroceryList struct {
Fruit struct {
Bananas int `default:"8"`
Pears int `default:"12"`
}
Vegetables *struct {
Artichokes int `default:"4"`
SweetPotatoes int `default:"16"`
}
}
```
Embedded structs do not need a `default` tag in order to be parsed. Embedded
structs that are `nil` will be initialized with their zero value so they can be
parsed accoringly.
### Runes and Int32s
In Go `rune` is just an alias for `int32`. This presents some ambiguity when
parsing default values. For example, should `"1"` be parsed as a literal `1` or
as a unicode `'1'` (which has the `int32` value of `49`)?
Because of this ambiguity we recommend avoiding setting defaults on `rune`s.
That said, this package defaults to parsing `int32` as integers. Failing that,
it tries to parse them as a `rune`.
```go
// This works as expected...
type Cool struct {
Fave32BitInteger int32 `default:"12"`
FaveChar rune `default:"a"`
}
// ...but these will not.
type UhOh struct {
FaveChar rune `default:"3"` // this is a unicode ETX or ctrl+c
FaveChar rune `default:"97"` // this is a unicode `a`
}
```
## Licnse
[MIT](https://github.com/meowgorithm/defaults/raw/master/LICENSE)