https://github.com/fredbi/gflag
go-generics implementation of CLI flags
https://github.com/fredbi/gflag
cli flags
Last synced: 6 months ago
JSON representation
go-generics implementation of CLI flags
- Host: GitHub
- URL: https://github.com/fredbi/gflag
- Owner: fredbi
- License: apache-2.0
- Created: 2022-11-21T11:23:17.000Z (over 3 years ago)
- Default Branch: master
- Last Pushed: 2023-09-29T14:27:58.000Z (almost 3 years ago)
- Last Synced: 2025-04-02T04:11:24.259Z (over 1 year ago)
- Topics: cli, flags
- Language: Go
- Homepage:
- Size: 53.7 KB
- Stars: 3
- Watchers: 2
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
- Codeowners: .github/CODEOWNERS
Awesome Lists containing this project
README
[](https://coveralls.io/github/fredbi/gflag)
[](https://goreportcard.com/report/github.com/fredbi/gflag)
[](https://pkg.go.dev/github.com/fredbi/gflag)
[](https://raw.githubusercontent.com/fredbi/go-cli/master/LICENSE.md)
# gflag
`pflags` with generic types.
> OK so this is yet another CLI flags library...
>
> We do not reinvent the wheel: this module reuses the great package `github.com/spf13/pflag`,
> with an interface built on go generics.
>
> The main idea is to simplify the `pflag` interface, with less things to remember about flag types.
>
> So this is not a fork or drop-in replacement, but rather an extension of the `pflag` functionality.
## Usage
This package is designed to be used together with `github.com/spf13/pflag`.
All types created by `gflag` implement the `pflag.Value` interface.
Use-case: build idiomatic `cobra` CLIs with a simpler declaration of flags.
See how [go-cli](https://github.com/fredbi/go-cli) achieves this.
```go
import (
"fmt"
"github.com/fredbi/gflag"
"github.com/spf13/pflag"
)
var flagVal int
fs := pflag.NewFlagSet("", pflag.ContinueOnError)
intFlag := gflag.NewFlagValue(&flagVal, 1) // infer flag from underlying type int, with a default value
fs.Var(intFlag, "integer", "integer value") // register the flag in pflag flagset
_ = fs.Parse([]string{"--integer", 10}) // parse command line arguments
fmt.Println(intFlag.GetValue()) // the flag knows the type of the value
```
With `pflag` this piece of code would look very much similar.
```go
import (
"fmt"
"github.com/spf13/pflag"
)
var flagVal int
fs := pflag.NewFlagSet("", pflag.ContinueOnError)
fs.IntVar(&flagVal, "integer", "integer value") // register the flag in pflag flagset
_ = fs.Parse([]string{"--integer", 10}) // parse command line arguments
fmt.Println(fs.GetInt("integer")) // has to know an integer type is expected
```
You may take a look at [more examples](example_values_test.go), with slices and maps.
## What does this bring to the table?
This package provides a unified approach to strongly typed flags, using go generics.
This way, we no longer have to register CLI flags using dozen of type-specific methods, just three:
* `NewFlagValue()`: for scalar values
* `NewFlagSliceValue()`: for flags as lists
* `NewFlagMapValue()`: for flags as map (e.g. key=value pairs)
The flag building logic is **consistent** for single values, slices and maps of all types.
Differences in semantics are handled with a set of `Option`s.
* **All primitive types** (yes, complex too!) are supported.
* All common types handled by `pflag` (`time.Duration`, `net.IP`, etc..) are also supported.
* I have also added `time.Time`
* Support any extension built for `pflag` (arbitrary types with the `pflag.Value` interface)
Variations in the semantics for a flag with a given underlying type may be fine-tuned with options.
There is an `extensions` sub-package to contribute some custom extra flag types.
It is now populated with a `byte-size` flag. See [the example](extensions/example_test.go).
## [About CLI flags](./docs/about.md)