go-options

LaunchDarkly Options Generator

The LaunchDarkly Options Generator generates boilerplate code for setting options for a configuration struct using varargs syntax. You write this:

//go:generate go run github.com/pjoc-team/go-options config
type config struct {
	howMany int
}

Then run go generate and you can write this:

cfg, err := newConfig(OptionHowMany(100))

or, more interestingly, this:

type Collection {
    config
}

func NewCollection(options... Option) (Foo, err) {
    cfg, err := newConfig(options...)
    return Collection{cfg}, nil
}

You can also specify default values and override the option name as follows:

//go:generate go run github.com/pjoc-team/go-options config
type config struct {
	howMany int `options:"number,5"
}

This would create OptionNumber with a default value of 5. Entering the the tag options:",5" would keep the default OptionHowMany name.

You can also specify documentation using docstrings or line strings, so:

//go:generate go run github.com/pjoc-team/go-options config
type config struct {
    // indicates the number of items
    howMany int // no more than 10
}

would generate code that looks like this:

// OptionHowMany indicates the number of items
// no more than ten
func WithHowMany(o int) applyOptionFunc {
    // ...
}

You can use nested structures to create multi-field options, so:

type config struct {
    number struct {
        a, b int
    }
}

would yield:

func WithNumber(a int, b int) applyOptionFunc {
    // ...
}

You can use also use "..." at the end of a name in options tag to create variadic arguments, so:

type config struct {
  numbers []int `options:"..."`
  nums []int `options:"ints..."`
}

would yield:

func WithNumbers(numbers ...int) applyOptionFunc {
    // ...
}

func WithInts(nums ...int) applyOptionFunc {
    // ...
}

You can use also use "*" at the beginning of a name in options tag to record whether an option was set, so:

type config struct {
  value *int `options:"*"`
  v *int `options:"*myValue"`
}

would yield:

func WithValue(o ...int) applyOptionFunc {
    // ...
}

func WithMyValue(o ...int) applyOptionFunc {
    // ...
}

Generated options are interoperable with any other user-created options that support the option interface:

type Option interface {
    apply(config *c) error
}

The name Option can be customized along with various method names as shown under Options below.

Installation

Install with go get -u github.com/launchdarkly/go-options.

Tag Syntax

The syntax for a tag is:

<alternateName or blank>,[optional default value]

Options

go-options can be customized with several command-line arguments:

• -fmt=false disable running gofmt
• -func <string> sets the name of function created to apply options to (default is apply<Type>Options)
• -new=false controls generation of the function that returns a new config (default true)
• -imports=[<path>|<alias>=<path>],... add imports to generated file
• -option <string> sets name of the interface to use for options (default "Option")
• -output <string> sets the name of the output file (default is _options.go)
• -prefix <string> sets prefix to be used for options (defaults to the value of option)
• -quote-default-strings=false disables default quoting of default values for string
• -suffix <string> sets suffix to be used for options (instead of prefix, cannot be used with prefix option)
• -type <string> name of struct type to create options for (original syntax before multiple types on command-line were supported)