Convert Option to an interface and make Vars a map conforming to the interface.

.circleci/config.yml

@@ -12,7 +12,7 @@ jobs:
           command: |
             go get -v github.com/jstemmer/go-junit-report
             go get -v -t -d ./...
-            curl -sfL https://install.goreleaser.com/github.com/golangci/golangci-lint.sh | bash -s latest
+            curl -sfL https://install.goreleaser.com/github.com/golangci/golangci-lint.sh | bash -s v1.8
             mkdir ~/report
           when: always
       - run:

.golangci.yml

@@ -8,6 +8,7 @@ linters:
   enable-all: true
   disable:
     - maligned
+    - lll
 
 linters-settings:
   govet:

README.md

@@ -366,7 +366,7 @@ Variables are in the form:
 
     ${<name>}
 
-Variables are set with the `Vars(map[string]string)` option. Undefined
+Variables are set with the `Vars{"key": "value", ...}` option. Undefined
 variable references in the grammar will result in an error at construction
 time.
 
@@ -385,9 +385,9 @@ type cli struct {
 
 func main() {
   kong.Parse(&cli,
-    kong.Vars(map[string]string{
+    kong.Vars{
       "config_file": "~/.app.conf",
-    }))
+    })
 }
 ```
 

kong.go

@@ -72,7 +72,7 @@ func New(grammar interface{}, options ...Option) (*Kong, error) {
 	}
 
 	for _, option := range options {
-		if err := option(k); err != nil {
+		if err := option.Apply(k); err != nil {
 			return nil, err
 		}
 	}
@@ -90,7 +90,7 @@ func New(grammar interface{}, options ...Option) (*Kong, error) {
 	k.Model.HelpFlag = k.helpFlag
 
 	for _, option := range k.postBuildOptions {
-		if err = option(k); err != nil {
+		if err = option.Apply(k); err != nil {
 			return nil, err
 		}
 	}

kong_test.go

@@ -520,11 +520,11 @@ func TestInterpolationIntoModel(t *testing.T) {
 	}
 	_, err := kong.New(&cli)
 	require.Error(t, err)
-	p, err := kong.New(&cli, kong.Vars(map[string]string{
+	p, err := kong.New(&cli, kong.Vars{
 		"default":  "Some default value.",
 		"somebody": "chickens!",
 		"enum":     "a,b,c,d",
-	}))
+	})
 	require.NoError(t, err)
 	flag := p.Model.Flags[1]
 	flag2 := p.Model.Flags[2]

mapper.go

@@ -150,7 +150,7 @@ func (r *Registry) RegisterKind(kind reflect.Kind, mapper Mapper) *Registry {
 	return r
 }
 
-// RegisterName registeres a mapper to be used if the value mapper has a "type" tag matching name.
+// RegisterName registers a mapper to be used if the value mapper has a "type" tag matching name.
 //
 // eg.
 //

options.go

@@ -10,20 +10,28 @@ import (
 )
 
 // An Option applies optional changes to the Kong application.
-type Option func(k *Kong) error
+type Option interface {
+	Apply(k *Kong) error
+}
+
+// OptionFunc is function that adheres to the Option interface.
+type OptionFunc func(k *Kong) error
+
+func (o OptionFunc) Apply(k *Kong) error { return o(k) } // nolint: golint
 
 // Vars sets the variables to use for interpolation into help strings and default values.
 //
 // See README for details.
-func Vars(vars map[string]string) Option {
+type Vars map[string]string
-	return func(k *Kong) error {
+
-		k.vars = vars
+// Apply lets Vars act as an Option.
-		return nil
+func (v Vars) Apply(k *Kong) error {
-	}
+	k.vars = v
+	return nil
 }
 
 // Exit overrides the function used to terminate. This is useful for testing or interactive use.
-func Exit(exit func(int)) Option {
+func Exit(exit func(int)) OptionFunc {
 	return func(k *Kong) error {
 		k.Exit = exit
 		return nil
@@ -31,7 +39,7 @@ func Exit(exit func(int)) Option {
 }
 
 // NoDefaultHelp disables the default help flags.
-func NoDefaultHelp() Option {
+func NoDefaultHelp() OptionFunc {
 	return func(k *Kong) error {
 		k.noDefaultHelp = true
 		return nil
@@ -39,29 +47,29 @@ func NoDefaultHelp() Option {
 }
 
 // Name overrides the application name.
-func Name(name string) Option {
+func Name(name string) OptionFunc {
 	return func(k *Kong) error {
-		k.postBuildOptions = append(k.postBuildOptions, func(k *Kong) error {
+		k.postBuildOptions = append(k.postBuildOptions, OptionFunc(func(k *Kong) error {
 			k.Model.Name = name
 			return nil
-		})
+		}))
 		return nil
 	}
 }
 
 // Description sets the application description.
-func Description(description string) Option {
+func Description(description string) OptionFunc {
 	return func(k *Kong) error {
-		k.postBuildOptions = append(k.postBuildOptions, func(k *Kong) error {
+		k.postBuildOptions = append(k.postBuildOptions, OptionFunc(func(k *Kong) error {
 			k.Model.Help = description
 			return nil
-		})
+		}))
 		return nil
 	}
 }
 
 // TypeMapper registers a mapper to a type.
-func TypeMapper(typ reflect.Type, mapper Mapper) Option {
+func TypeMapper(typ reflect.Type, mapper Mapper) OptionFunc {
 	return func(k *Kong) error {
 		k.registry.RegisterType(typ, mapper)
 		return nil
@@ -69,7 +77,7 @@ func TypeMapper(typ reflect.Type, mapper Mapper) Option {
 }
 
 // KindMapper registers a mapper to a kind.
-func KindMapper(kind reflect.Kind, mapper Mapper) Option {
+func KindMapper(kind reflect.Kind, mapper Mapper) OptionFunc {
 	return func(k *Kong) error {
 		k.registry.RegisterKind(kind, mapper)
 		return nil
@@ -77,7 +85,7 @@ func KindMapper(kind reflect.Kind, mapper Mapper) Option {
 }
 
 // ValueMapper registers a mapper to a field value.
-func ValueMapper(ptr interface{}, mapper Mapper) Option {
+func ValueMapper(ptr interface{}, mapper Mapper) OptionFunc {
 	return func(k *Kong) error {
 		k.registry.RegisterValue(ptr, mapper)
 		return nil
@@ -85,7 +93,7 @@ func ValueMapper(ptr interface{}, mapper Mapper) Option {
 }
 
 // NamedMapper registers a mapper to a name.
-func NamedMapper(name string, mapper Mapper) Option {
+func NamedMapper(name string, mapper Mapper) OptionFunc {
 	return func(k *Kong) error {
 		k.registry.RegisterName(name, mapper)
 		return nil
@@ -93,7 +101,7 @@ func NamedMapper(name string, mapper Mapper) Option {
 }
 
 // Writers overrides the default writers. Useful for testing or interactive use.
-func Writers(stdout, stderr io.Writer) Option {
+func Writers(stdout, stderr io.Writer) OptionFunc {
 	return func(k *Kong) error {
 		k.Stdout = stdout
 		k.Stderr = stderr
@@ -112,7 +120,7 @@ type HookFunc func(ctx *Context, path *Path) error
 //
 // Note that the hook will be called once for each time the corresponding node is encountered. This means that if a flag
 // is passed twice, its hook will be called twice.
-func Hook(ptr interface{}, hook HookFunc) Option {
+func Hook(ptr interface{}, hook HookFunc) OptionFunc {
 	key := reflect.ValueOf(ptr)
 	if key.Kind() != reflect.Ptr {
 		panic("expected a pointer")
@@ -124,7 +132,7 @@ func Hook(ptr interface{}, hook HookFunc) Option {
 }
 
 // Help printer to use.
-func Help(help HelpPrinter) Option {
+func Help(help HelpPrinter) OptionFunc {
 	return func(k *Kong) error {
 		k.help = help
 		return nil
@@ -132,7 +140,7 @@ func Help(help HelpPrinter) Option {
 }
 
 // ConfigureHelp sets the HelpOptions to use for printing help.
-func ConfigureHelp(options HelpOptions) Option {
+func ConfigureHelp(options HelpOptions) OptionFunc {
 	return func(k *Kong) error {
 		k.helpOptions = options
 		return nil
@@ -140,7 +148,7 @@ func ConfigureHelp(options HelpOptions) Option {
 }
 
 // UsageOnError configures Kong to display context-sensitive usage if FatalIfErrorf is called with an error.
-func UsageOnError() Option {
+func UsageOnError() OptionFunc {
 	return func(k *Kong) error {
 		k.usageOnError = true
 		return nil
@@ -148,7 +156,7 @@ func UsageOnError() Option {
 }
 
 // ClearResolvers clears all existing resolvers.
-func ClearResolvers() Option {
+func ClearResolvers() OptionFunc {
 	return func(k *Kong) error {
 		k.resolvers = nil
 		return nil
@@ -156,7 +164,7 @@ func ClearResolvers() Option {
 }
 
 // Resolver registers flag resolvers.
-func Resolver(resolvers ...ResolverFunc) Option {
+func Resolver(resolvers ...ResolverFunc) OptionFunc {
 	return func(k *Kong) error {
 		k.resolvers = append(k.resolvers, resolvers...)
 		return nil
@@ -173,7 +181,7 @@ type ConfigurationFunc func(r io.Reader) (ResolverFunc, error)
 // Note: The JSON function is a ConfigurationFunc.
 //
 // ~ expansion will occur on the provided paths.
-func Configuration(loader ConfigurationFunc, paths ...string) Option {
+func Configuration(loader ConfigurationFunc, paths ...string) OptionFunc {
 	return func(k *Kong) error {
 		for _, path := range paths {
 			path = expandPath(path)