dig

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Published: Oct 19, 2023 License: MIT Imports: 16 Imported by: 1,122

README

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A reflection based dependency injection toolkit for Go.

Good for:
  • Powering an application framework, e.g. Fx.
  • Resolving the object graph during process startup.
Bad for:
  • Using in place of an application framework, e.g. Fx.
  • Resolving dependencies after the process has already started.
  • Exposing to user-land code as a Service Locator.

Installation

We recommend consuming SemVer major version 1 using your dependency manager of choice.

$ glide get 'go.uber.org/dig#^1'
$ dep ensure -add "go.uber.org/dig@v1"
$ go get 'go.uber.org/dig@v1'

Stability

This library is v1 and follows SemVer strictly.

No breaking changes will be made to exported APIs before v2.0.0.

Stargazers over time

Stargazers over time

Documentation

Overview

Package dig provides an opinionated way of resolving object dependencies.

Status

STABLE. No breaking changes will be made in this major version.

Container

Dig exposes type Container as an object capable of resolving a directed acyclic dependency graph. Use the New function to create one.

c := dig.New()

Provide

Constructors for different types are added to the container by using the Provide method. A constructor can declare a dependency on another type by simply adding it as a function parameter. Dependencies for a type can be added to the graph both, before and after the type was added.

err := c.Provide(func(conn *sql.DB) (*UserGateway, error) {
  // ...
})
if err != nil {
  // ...
}

if err := c.Provide(newDBConnection); err != nil {
  // ...
}

Multiple constructors can rely on the same type. The container creates a singleton for each retained type, instantiating it at most once when requested directly or as a dependency of another type.

err := c.Provide(func(conn *sql.DB) *CommentGateway {
  // ...
})
if err != nil {
  // ...
}

Constructors can declare any number of dependencies as parameters and optionally, return errors.

err := c.Provide(func(u *UserGateway, c *CommentGateway) (*RequestHandler, error) {
  // ...
})
if err != nil {
  // ...
}

if err := c.Provide(newHTTPServer); err != nil {
  // ...
}

Constructors can also return multiple results to add multiple types to the container.

err := c.Provide(func(conn *sql.DB) (*UserGateway, *CommentGateway, error) {
  // ...
})
if err != nil {
  // ...
}

Constructors that accept a variadic number of arguments are treated as if they don't have those arguments. That is,

func NewVoteGateway(db *sql.DB, options ...Option) *VoteGateway

Is treated the same as,

func NewVoteGateway(db *sql.DB) *VoteGateway

The constructor will be called with all other dependencies and no variadic arguments.

Invoke

Types added to the container may be consumed by using the Invoke method. Invoke accepts any function that accepts one or more parameters and optionally, returns an error. Dig calls the function with the requested type, instantiating only those types that were requested by the function. The call fails if any type or its dependencies (both direct and transitive) were not available in the container.

err := c.Invoke(func(l *log.Logger) {
  // ...
})
if err != nil {
  // ...
}

err := c.Invoke(func(server *http.Server) error {
  // ...
})
if err != nil {
  // ...
}

Any error returned by the invoked function is propagated back to the caller.

Parameter Objects

Constructors declare their dependencies as function parameters. This can very quickly become unreadable if the constructor has a lot of dependencies.

func NewHandler(users *UserGateway, comments *CommentGateway, posts *PostGateway, votes *VoteGateway, authz *AuthZGateway) *Handler {
  // ...
}

A pattern employed to improve readability in a situation like this is to create a struct that lists all the parameters of the function as fields and changing the function to accept that struct instead. This is referred to as a parameter object.

Dig has first class support for parameter objects: any struct embedding dig.In gets treated as a parameter object. The following is equivalent to the constructor above.

type HandlerParams struct {
  dig.In

  Users    *UserGateway
  Comments *CommentGateway
  Posts    *PostGateway
  Votes    *VoteGateway
  AuthZ    *AuthZGateway
}

func NewHandler(p HandlerParams) *Handler {
  // ...
}

Handlers can receive any combination of parameter objects and parameters.

func NewHandler(p HandlerParams, l *log.Logger) *Handler {
  // ...
}

Result Objects

Result objects are the flip side of parameter objects. These are structs that represent multiple outputs from a single function as fields in the struct. Structs embedding dig.Out get treated as result objects.

func SetupGateways(conn *sql.DB) (*UserGateway, *CommentGateway, *PostGateway, error) {
  // ...
}

The above is equivalent to,

type Gateways struct {
  dig.Out

  Users    *UserGateway
  Comments *CommentGateway
  Posts    *PostGateway
}

func SetupGateways(conn *sql.DB) (Gateways, error) {
  // ...
}

Optional Dependencies

Constructors often don't have a hard dependency on some types and are able to operate in a degraded state when that dependency is missing. Dig supports declaring dependencies as optional by adding an `optional:"true"` tag to fields of a dig.In struct.

Fields in a dig.In structs that have the `optional:"true"` tag are treated as optional by Dig.

type UserGatewayParams struct {
  dig.In

  Conn  *sql.DB
  Cache *redis.Client `optional:"true"`
}

If an optional field is not available in the container, the constructor will receive a zero value for the field.

func NewUserGateway(p UserGatewayParams, log *log.Logger) (*UserGateway, error) {
  if p.Cache == nil {
    log.Print("Caching disabled")
  }
  // ...
}

Constructors that declare dependencies as optional MUST handle the case of those dependencies being absent.

The optional tag also allows adding new dependencies without breaking existing consumers of the constructor.

Named Values

Some use cases call for multiple values of the same type. Dig allows adding multiple values of the same type to the container with the use of Named Values.

Named Values can be produced by passing the dig.Name option when a constructor is provided. All values produced by that constructor will have the given name.

Given the following constructors,

func NewReadOnlyConnection(...) (*sql.DB, error)
func NewReadWriteConnection(...) (*sql.DB, error)

You can provide *sql.DB into a Container under different names by passing the dig.Name option.

c.Provide(NewReadOnlyConnection, dig.Name("ro"))
c.Provide(NewReadWriteConnection, dig.Name("rw"))

Alternatively, you can produce a dig.Out struct and tag its fields with `name:".."` to have the corresponding value added to the graph under the specified name.

type ConnectionResult struct {
  dig.Out

  ReadWrite *sql.DB `name:"rw"`
  ReadOnly  *sql.DB `name:"ro"`
}

func ConnectToDatabase(...) (ConnectionResult, error) {
  // ...
  return ConnectionResult{ReadWrite: rw, ReadOnly:  ro}, nil
}

Regardless of how a Named Value was produced, it can be consumed by another constructor by accepting a dig.In struct which has exported fields with the same name AND type that you provided.

type GatewayParams struct {
  dig.In

  WriteToConn  *sql.DB `name:"rw"`
  ReadFromConn *sql.DB `name:"ro"`
}

The name tag may be combined with the optional tag to declare the dependency optional.

type GatewayParams struct {
  dig.In

  WriteToConn  *sql.DB `name:"rw"`
  ReadFromConn *sql.DB `name:"ro" optional:"true"`
}

func NewCommentGateway(p GatewayParams, log *log.Logger) (*CommentGateway, error) {
  if p.ReadFromConn == nil {
    log.Print("Warning: Using RW connection for reads")
    p.ReadFromConn = p.WriteToConn
  }
  // ...
}

Value Groups

Added in Dig 1.2.

Dig provides value groups to allow producing and consuming many values of the same type. Value groups allow constructors to send values to a named, unordered collection in the container. Other constructors can request all values in this collection as a slice.

Constructors can send values into value groups by returning a dig.Out struct tagged with `group:".."`.

type HandlerResult struct {
  dig.Out

  Handler Handler `group:"server"`
}

func NewHelloHandler() HandlerResult {
  ..
}

func NewEchoHandler() HandlerResult {
  ..
}

Any number of constructors may provide values to this named collection. Other constructors can request all values for this collection by requesting a slice tagged with `group:".."`. This will execute all constructors that provide a value to that group in an unspecified order.

type ServerParams struct {
  dig.In

  Handlers []Handler `group:"server"`
}

func NewServer(p ServerParams) *Server {
  server := newServer()
  for _, h := range p.Handlers {
    server.Register(h)
  }
  return server
}

Note that values in a value group are unordered. Dig makes no guarantees about the order in which these values will be produced.

Value groups can be used to provide multiple values for a group from a dig.Out using slices, however considering groups are retrieved by requesting a slice this implies that the values must be retrieved using a slice of slices. As of dig v1.9.0, if you want to provide individual elements to the group instead of the slice itself, you can add the `flatten` modifier to the group from a dig.Out.

type IntResult struct {
  dig.Out

  Handler []int `group:"server"`         // [][]int from dig.In
  Handler []int `group:"server,flatten"` // []int from dig.In
}
Example (Minimal)
package main

import (
	"encoding/json"
	"log"
	"os"

	"go.uber.org/dig"
)

func main() {
	type Config struct {
		Prefix string
	}

	c := dig.New()

	// Provide a Config object. This can fail to decode.
	err := c.Provide(func() (*Config, error) {
		// In a real program, the configuration will probably be read from a
		// file.
		var cfg Config
		err := json.Unmarshal([]byte(`{"prefix": "[foo] "}`), &cfg)
		return &cfg, err
	})
	if err != nil {
		panic(err)
	}

	// Provide a way to build the logger based on the configuration.
	err = c.Provide(func(cfg *Config) *log.Logger {
		return log.New(os.Stdout, cfg.Prefix, 0)
	})
	if err != nil {
		panic(err)
	}

	// Invoke a function that requires the logger, which in turn builds the
	// Config first.
	err = c.Invoke(func(l *log.Logger) {
		l.Print("You've been invoked")
	})
	if err != nil {
		panic(err)
	}

}
Output:

[foo] You've been invoked

Index

Examples

Constants

View Source
const Version = "1.17.1"

Version of the library.

Variables

This section is empty.

Functions

func CanVisualizeError added in v1.4.0

func CanVisualizeError(err error) bool

CanVisualizeError returns true if the error is an errVisualizer.

func IsCycleDetected added in v1.5.0

func IsCycleDetected(err error) bool

IsCycleDetected returns a boolean as to whether the provided error indicates a cycle was detected in the container graph.

func IsIn added in v1.0.0

func IsIn(o interface{}) bool

IsIn checks whether the given struct is a dig.In struct. A struct qualifies as a dig.In struct if it embeds the dig.In type or if any struct that it embeds is a dig.In struct. The parameter may be the reflect.Type of the struct rather than the struct itself.

A struct MUST qualify as a dig.In struct for its fields to be treated specially by dig.

See the documentation for dig.In for a comprehensive list of supported tags.

func IsOut added in v1.0.0

func IsOut(o interface{}) bool

IsOut checks whether the given struct is a dig.Out struct. A struct qualifies as a dig.Out struct if it embeds the dig.Out type or if any struct that it embeds is a dig.Out struct. The parameter may be the reflect.Type of the struct rather than the struct itself.

A struct MUST qualify as a dig.Out struct for its fields to be treated specially by dig.

See the documentation for dig.Out for a comprehensive list of supported tags.

func RootCause added in v1.1.0

func RootCause(err error) error

RootCause returns the first non-dig.Error in a chain of wrapped errors, if there is one. Otherwise, RootCause returns the error on the bottom of the chain of wrapped errors.

Use this function and errors.As to differentiate between Dig errors and errors thrown by provided constructors or invoked functions:

rootCause := dig.RootCause(err)
var de dig.Error
if errors.As(rootCause, &de) {
    // Is a Dig error
} else {
    // Is an error thrown by one of my provided/invoked/decorated functions
}

See PanicError for an example showing how to additionally detect and handle panics in provided/invoked/decorated functions.

func Visualize added in v1.4.0

func Visualize(c *Container, w io.Writer, opts ...VisualizeOption) error

Visualize parses the graph in Container c into DOT format and writes it to io.Writer w.

Types

type Callback added in v1.17.0

type Callback func(CallbackInfo)

Callback is a function that can be registered with a provided function or decorator with [WithCallback] to cause it to be called after the provided function or decorator is run.

type CallbackInfo added in v1.17.0

type CallbackInfo struct {

	// Name is the name of the function in the format:
	// <package_name>.<function_name>
	Name string

	// Error contains the error returned by the [Callback]'s associated
	// function, if any. When used in conjunction with [RecoverFromPanics],
	// this will be set to a [PanicError] when the function panics.
	Error error
}

CallbackInfo contains information about a provided function or decorator called by Dig, and is passed to a Callback registered with WithProviderCallback or WithDecoratorCallback.

type Container

type Container struct {
	// contains filtered or unexported fields
}

Container is a directed acyclic graph of types and their dependencies. A Container is the root Scope that represents the top-level scoped directed acyclic graph of the dependencies.

func New

func New(opts ...Option) *Container

New constructs a Container.

func (*Container) Decorate added in v1.14.0

func (c *Container) Decorate(decorator interface{}, opts ...DecorateOption) error

Decorate provides a decorator for a type that has already been provided in the Container. Decorations at this level affect all scopes of the container. See Scope.Decorate for information on how to use this method.

func (*Container) Invoke

func (c *Container) Invoke(function interface{}, opts ...InvokeOption) error

Invoke runs the given function after instantiating its dependencies.

Any arguments that the function has are treated as its dependencies. The dependencies are instantiated in an unspecified order along with any dependencies that they might have.

The function may return an error to indicate failure. The error will be returned to the caller as-is.

If the RecoverFromPanics option was given to the container and a panic occurs when invoking, a PanicError with the panic contained will be returned. See PanicError for more info.

func (*Container) Provide

func (c *Container) Provide(constructor interface{}, opts ...ProvideOption) error

Provide teaches the container how to build values of one or more types and expresses their dependencies.

The first argument of Provide is a function that accepts zero or more parameters and returns one or more results. The function may optionally return an error to indicate that it failed to build the value. This function will be treated as the constructor for all the types it returns. This function will be called AT MOST ONCE when a type produced by it, or a type that consumes this function's output, is requested via Invoke. If the same types are requested multiple times, the previously produced value will be reused.

Provide accepts argument types or dig.In structs as dependencies, and separate return values or dig.Out structs for results.

func (*Container) Scope added in v1.14.0

func (c *Container) Scope(name string, opts ...ScopeOption) *Scope

Scope creates a child scope of the Container with the given name.

func (*Container) String

func (c *Container) String() string

String representation of the entire Container

type DecorateInfo added in v1.14.0

type DecorateInfo struct {
	ID      ID
	Inputs  []*Input
	Outputs []*Output
}

DecorateInfo provides information about the decorator's inputs and outputs types as strings, as well as the ID of the decorator supplied to the Container.

type DecorateOption added in v1.14.0

type DecorateOption interface {
	// contains filtered or unexported methods
}

DecorateOption modifies the default behavior of Decorate.

func FillDecorateInfo added in v1.14.0

func FillDecorateInfo(info *DecorateInfo) DecorateOption

FillDecorateInfo is a DecorateOption that writes info on what Dig was able to get out of the provided decorator into the provided DecorateInfo.

func WithDecoratorCallback added in v1.17.0

func WithDecoratorCallback(callback Callback) DecorateOption

WithDecoratorCallback returns a DecorateOption which has Dig call the passed in Callback after the corresponding decorator finishes running.

For example, the following prints a completion message after "myDecorator" finishes, including the error if any:

c := dig.New()
myCallback := func(ci CallbackInfo) {
	var errorAdd string
	if ci.Error != nil {
		errorAdd = fmt.Sprintf("with error: %v", ci.Error)
	}
	fmt.Printf("%q finished%v", ci.Name, errorAdd)
}
c.Decorate(myDecorator, WithDecoratorCallback(myCallback)),

Callbacks can also be specified for Constructors with WithProviderCallback.

See CallbackInfo for more info on the information passed to the Callback.

type Error added in v1.16.0

type Error interface {
	error
	// contains filtered or unexported methods
}

Error is an interface implemented by all Dig errors.

Use this interface, in conjunction with RootCause, in order to determine if errors you encounter come from Dig, or if they come from provided constructors or invoked functions. See RootCause for more info.

type ID added in v1.12.0

type ID int

ID is a unique integer representing the constructor node in the dependency graph.

type In

type In struct {
	// contains filtered or unexported fields
}

In may be embedded into structs to request dig to treat them as special parameter structs. When a constructor accepts such a struct, instead of the struct becoming a dependency for that constructor, all its fields become dependencies instead. See the section on Parameter Objects in the package-level documentation for more information.

Fields of the struct may optionally be tagged to customize the behavior of dig. The following tags are supported,

name        Requests a value with the same name and type from the
            container. See Named Values for more information.
optional    If set to true, indicates that the dependency is optional and
            the constructor gracefully handles its absence.
group       Name of the Value Group from which this field will be filled.
            The field must be a slice type. See Value Groups in the
            package documentation for more information.

type Input added in v1.12.0

type Input struct {
	// contains filtered or unexported fields
}

Input contains information on an input parameter of a function.

func (*Input) String added in v1.12.0

func (i *Input) String() string

type InvokeInfo added in v1.17.0

type InvokeInfo struct {
	Inputs []*Input
}

InvokeInfo provides information about an Invoke.

type InvokeOption added in v1.0.0

type InvokeOption interface {
	// contains filtered or unexported methods
}

An InvokeOption modifies the default behavior of Invoke.

func FillInvokeInfo added in v1.17.0

func FillInvokeInfo(info *InvokeInfo) InvokeOption

FillInvokeInfo is an InvokeOption that writes information on the types accepted by the Invoke function into the specified InvokeInfo. For example:

		var info dig.InvokeInfo
		err := c.Invoke(func(string, int){}, dig.FillInvokeInfo(&info))

  info.Inputs[0].String() will be string.
  info.Inputs[1].String() will be int.

type Option added in v1.0.0

type Option interface {
	// contains filtered or unexported methods
}

Option configures a Container.

func DeferAcyclicVerification added in v1.5.0

func DeferAcyclicVerification() Option

DeferAcyclicVerification is an Option to override the default behavior of container.Provide, deferring the dependency graph validation to no longer run after each call to container.Provide. The container will instead verify the graph on first `Invoke`.

Applications adding providers to a container in a tight loop may experience performance improvements by initializing the container with this option.

func DryRun added in v1.10.0

func DryRun(dry bool) Option

DryRun is an Option which, when set to true, disables invocation of functions supplied to Provide and Invoke. Use this to build no-op containers.

func RecoverFromPanics added in v1.16.0

func RecoverFromPanics() Option

RecoverFromPanics is an Option to recover from panics that occur while running functions given to the container. When set, recovered panics will be placed into a PanicError, and returned at the invoke callsite. See PanicError for an example on how to handle panics with this option enabled, and distinguish them from errors.

type Out

type Out struct {
	// contains filtered or unexported fields
}

Out may be embedded into structs to request dig to treat them as special result structs. When a constructor returns such a struct, instead of the struct becoming a result of the constructor, all its fields become results of the constructor. See the section on Result Objects in the package-level documentation for more information.

Fields of the struct may optionally be tagged to customize the behavior of dig. The following tags are supported,

name        Specifies the name of the value. Only a field on a dig.In
            struct with the same 'name' annotation can receive this
            value. See Named Values for more information.
group       Name of the Value Group to which this field's value is being
            sent. See Value Groups in the package documentation for more
            information.

type Output added in v1.12.0

type Output struct {
	// contains filtered or unexported fields
}

Output contains information on an output produced by a function.

func (*Output) String added in v1.12.0

func (o *Output) String() string

type PanicError added in v1.16.0

type PanicError struct {

	// The panic that was returned from recover()
	Panic any
	// contains filtered or unexported fields
}

A PanicError occurs when a panic occurs while running functions given to the container with the [RecoverFromPanic] option being set. It contains the panic message from the original panic. A PanicError does not wrap other errors, and it does not implement dig.Error, meaning it will be returned from RootCause. With the [RecoverFromPanic] option set, a panic can be distinguished from dig errors and errors from provided/ invoked/decorated functions like so:

rootCause := dig.RootCause(err)

var pe dig.PanicError
var de dig.Error
if errors.As(rootCause, &pe) {
	// This is caused by a panic
} else if errors.As(err, &de) {
	// This is a dig error
} else {
	// This is an error from one of my provided/invoked functions or decorators
}

Or, if only interested in distinguishing panics from errors:

var pe dig.PanicError
if errors.As(err, &pe) {
	// This is caused by a panic
} else {
	// This is an error
}

func (PanicError) Error added in v1.16.0

func (e PanicError) Error() string

func (PanicError) Format added in v1.16.0

func (e PanicError) Format(w fmt.State, c rune)

Format will format the PanicError, expanding the corresponding function if in +v mode.

type ProvideInfo added in v1.12.0

type ProvideInfo struct {
	ID      ID
	Inputs  []*Input
	Outputs []*Output
}

ProvideInfo provides information about the constructor's inputs and outputs types as strings, as well as the ID of the constructor supplied to the Container. It contains ID for the constructor, as well as slices of Input and Output types, which are Stringers that report the types of the parameters and results respectively.

type ProvideOption added in v1.0.0

type ProvideOption interface {
	// contains filtered or unexported methods
}

A ProvideOption modifies the default behavior of Provide.

func As added in v1.13.0

func As(i ...interface{}) ProvideOption

As is a ProvideOption that specifies that the value produced by the constructor implements one or more other interfaces and is provided to the container as those interfaces.

As expects one or more pointers to the implemented interfaces. Values produced by constructors will be then available in the container as implementations of all of those interfaces, but not as the value itself.

For example, the following will make io.Reader and io.Writer available in the container, but not buffer.

c.Provide(newBuffer, dig.As(new(io.Reader), new(io.Writer)))

That is, the above is equivalent to the following.

c.Provide(func(...) (io.Reader, io.Writer) {
  b := newBuffer(...)
  return b, b
})

If used with dig.Name, the type produced by the constructor and the types specified with dig.As will all use the same name. For example,

c.Provide(newFile, dig.As(new(io.Reader)), dig.Name("temp"))

The above is equivalent to the following.

type Result struct {
  dig.Out

  Reader io.Reader `name:"temp"`
}

c.Provide(func(...) Result {
  f := newFile(...)
  return Result{
    Reader: f,
  }
})

This option cannot be provided for constructors which produce result objects.

func Export added in v1.14.0

func Export(export bool) ProvideOption

Export is a ProvideOption which specifies that the provided function should be made available to all Scopes available in the application, regardless of which Scope it was provided from. By default, it is false.

For example,

c := New()
s1 := c.Scope("child 1")
s2:= c.Scope("child 2")
s1.Provide(func() *bytes.Buffer { ... })

does not allow the constructor returning *bytes.Buffer to be made available to the root Container c or its sibling Scope s2.

With Export, you can make this constructor available to all the Scopes:

s1.Provide(func() *bytes.Buffer { ... }, Export(true))

func FillProvideInfo added in v1.12.0

func FillProvideInfo(info *ProvideInfo) ProvideOption

FillProvideInfo is a ProvideOption that writes info on what Dig was able to get out of the provided constructor into the provided ProvideInfo.

func Group added in v1.7.0

func Group(group string) ProvideOption

Group is a ProvideOption that specifies that all values produced by a constructor should be added to the specified group. See also the package documentation about Value Groups.

This option cannot be provided for constructors which produce result objects.

func LocationForPC added in v1.13.0

func LocationForPC(pc uintptr) ProvideOption

LocationForPC is a ProvideOption which specifies an alternate function program counter address to be used for debug information. The package, name, file and line number of this alternate function address will be used in error messages and DOT graphs. This option is intended to be used with functions created with the reflect.MakeFunc method whose error messages are otherwise hard to understand

func Name added in v1.4.0

func Name(name string) ProvideOption

Name is a ProvideOption that specifies that all values produced by a constructor should have the given name. See also the package documentation about Named Values.

Given,

func NewReadOnlyConnection(...) (*Connection, error)
func NewReadWriteConnection(...) (*Connection, error)

The following will provide two connections to the container: one under the name "ro" and the other under the name "rw".

c.Provide(NewReadOnlyConnection, dig.Name("ro"))
c.Provide(NewReadWriteConnection, dig.Name("rw"))

This option cannot be provided for constructors which produce result objects.

func WithProviderCallback added in v1.17.0

func WithProviderCallback(callback Callback) ProvideOption

WithProviderCallback returns a ProvideOption which has Dig call the passed in Callback after the corresponding constructor finishes running.

For example, the following prints a completion message after "myConstructor" finishes, including the error if any:

c := dig.New()
myCallback := func(ci CallbackInfo) {
	var errorAdd string
	if ci.Error != nil {
		errorAdd = fmt.Sprintf("with error: %v", ci.Error)
	}
	fmt.Printf("%q finished%v", ci.Name, errorAdd)
}
c.Provide(myConstructor, WithProviderCallback(myCallback)),

Callbacks can also be specified for Decorators with WithDecoratorCallback.

See CallbackInfo for more info on the information passed to the Callback.

type Scope added in v1.14.0

type Scope struct {
	// contains filtered or unexported fields
}

Scope is a scoped DAG of types and their dependencies. A Scope may also have one or more child Scopes that inherit from it.

func (*Scope) Decorate added in v1.14.0

func (s *Scope) Decorate(decorator interface{}, opts ...DecorateOption) error

Decorate provides a decorator for a type that has already been provided in the Scope.

Similar to Provide, Decorate takes in a function with zero or more dependencies and one or more results. Decorate can be used to modify a type that was already introduced to the Scope, or completely replace it with a new object.

For example,

s.Decorate(func(log *zap.Logger) *zap.Logger {
  return log.Named("myapp")
})

This takes in a value, augments it with a name, and returns a replacement for it. Functions in the Scope's dependency graph that use *zap.Logger will now use the *zap.Logger returned by this decorator.

A decorator can also take in multiple parameters and replace one of them:

s.Decorate(func(log *zap.Logger, cfg *Config) *zap.Logger {
  return log.Named(cfg.Name)
})

Or replace a subset of them:

s.Decorate(func(
  log *zap.Logger,
  cfg *Config,
  scope metrics.Scope
) (*zap.Logger, metrics.Scope) {
  log = log.Named(cfg.Name)
  scope = scope.With(metrics.Tag("service", cfg.Name))
  return log, scope
})

Decorating a Scope affects all the child scopes of this Scope.

Similar to a provider, the decorator function gets called *at most once*.

func (*Scope) Invoke added in v1.14.0

func (s *Scope) Invoke(function interface{}, opts ...InvokeOption) (err error)

Invoke runs the given function after instantiating its dependencies.

Any arguments that the function has are treated as its dependencies. The dependencies are instantiated in an unspecified order along with any dependencies that they might have.

The function may return an error to indicate failure. The error will be returned to the caller as-is.

func (*Scope) Provide added in v1.14.0

func (s *Scope) Provide(constructor interface{}, opts ...ProvideOption) error

Provide teaches the Scope how to build values of one or more types and expresses their dependencies.

The first argument of Provide is a function that accepts zero or more parameters and returns one or more results. The function may optionally return an error to indicate that it failed to build the value. This function will be treated as the constructor for all the types it returns. This function will be called AT MOST ONCE when a type produced by it, or a type that consumes this function's output, is requested via Invoke. If the same types are requested multiple times, the previously produced value will be reused.

Provide accepts argument types or dig.In structs as dependencies, and separate return values or dig.Out structs for results.

When a constructor is Provided to a Scope, it will propagate this to any Scopes that are descendents, but not ancestors of this Scope. To provide a constructor to all the Scopes available, provide it to Container, which is the root Scope.

func (*Scope) Scope added in v1.14.0

func (s *Scope) Scope(name string, opts ...ScopeOption) *Scope

Scope creates a new Scope with the given name and options from current Scope. Any constructors that the current Scope knows about, as well as any modifications made to it in the future will be propagated to the child scope. However, no modifications made to the child scope being created will be propagated to the parent Scope.

func (*Scope) String added in v1.14.0

func (s *Scope) String() string

String representation of the entire Scope

type ScopeOption added in v1.14.0

type ScopeOption interface {
	// contains filtered or unexported methods
}

A ScopeOption modifies the default behavior of Scope; currently, there are no implementations.

type VisualizeOption added in v1.4.0

type VisualizeOption interface {
	// contains filtered or unexported methods
}

A VisualizeOption modifies the default behavior of Visualize.

func VisualizeError added in v1.4.0

func VisualizeError(err error) VisualizeOption

VisualizeError includes a visualization of the given error in the output of Visualize if an error was returned by Invoke or Provide.

if err := c.Provide(...); err != nil {
  dig.Visualize(c, w, dig.VisualizeError(err))
}

This option has no effect if the error was nil or if it didn't contain any information to visualize.

Directories

Path Synopsis
internal
digtest
Package digtest provides utilities used by dig internally to test its own functionality.
Package digtest provides utilities used by dig internally to test its own functionality.
dot

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