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Alvaro Lopez Espinosa
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stringer.go
167
stringer.go
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@ -4,64 +4,147 @@
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// +build go1.5
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// Stringer is a tool to automate the creation of methods that satisfy the fmt.Stringer
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// interface. Given the name of a (signed or unsigned) integer type T that has constants
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// defined, stringer will create a new self-contained Go source file implementing
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// func (t T) String() string
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// The file is created in the same package and directory as the package that defines T.
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// It has helpful defaults designed for use with go generate.
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//# Enumer [](https://goreportcard.com/report/github.com/alvaroloes/enumer) 
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//Enumer is a tool to generate Go code that adds useful methods to Go enums (constants with a specific type).
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//It started as a fork of [Rob Pike’s Stringer tool](https://godoc.org/golang.org/x/tools/cmd/stringer).
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//
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// Stringer works best with constants that are consecutive values such as created using iota,
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// but creates good code regardless. In the future it might also provide custom support for
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// constant sets that are bit patterns.
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//## Generated functions and methods
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//When Enumer is applied to a type, it will generate:
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//
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// For example, given this snippet,
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//* The following basic methods/functions:
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//
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// package painkiller
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//* Method `String()`: returns the string representation of the enum value. This makes the enum conform
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//the `Stringer` interface, so whenever you print an enum value, you'll get the string name instead of a number.
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//* Function `<Type>String(s string)`: returns the enum value from its string representation. This is useful
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//when you need to read enum values from command line arguments, from a configuration file, or
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//from a REST API request... In short, from those places where using the real enum value (an integer) would
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//be almost meaningless or hard to trace or use by a human.
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//* Function `<Type>Values()`: returns a slice with all the values of the enum
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//* Method `IsA<Type>()`: returns true only if the current value is among the values of the enum. Useful for validations.
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//* When the flag `json` is provided, two additional methods will be generated, `MarshalJSON()` and `UnmarshalJSON()`. These make
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//the enum conform to the `json.Marshaler` and `json.Unmarshaler` interfaces. Very useful to use it in JSON APIs.
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//* When the flag `text` is provided, two additional methods will be generated, `MarshalText()` and `UnmarshalText()`. These make
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//the enum conform to the `encoding.TextMarshaler` and `encoding.TextUnmarshaler` interfaces.
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//**Note:** If you use your enum values as keys in a map and you encode the map as _JSON_, you need this flag set to true to properly
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//convert the map keys to json (strings). If not, the numeric values will be used instead
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//* When the flag `yaml` is provided, two additional methods will be generated, `MarshalYAML()` and `UnmarshalYAML()`. These make
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//the enum conform to the `gopkg.in/yaml.v2.Marshaler` and `gopkg.in/yaml.v2.Unmarshaler` interfaces.
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//* When the flag `sql` is provided, the methods for implementing the Scanner and Valuer interfaces will be also generated.
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//Useful when storing the enum in a database.
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//
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// type Pill int
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//For example, if we have an enum type called `Pill`,
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//```go
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//type Pill int
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//
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// const (
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// Placebo Pill = iota
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// Aspirin
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// Ibuprofen
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// Paracetamol
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// Acetaminophen = Paracetamol
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// )
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//const (
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// Placebo Pill = iota
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// Aspirin
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// Ibuprofen
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// Paracetamol
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// Acetaminophen = Paracetamol
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//)
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//```
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//executing `enumer -type=Pill -json` will generate a new file with four basic method and two extra for JSON:
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//```go
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//func (i Pill) String() string {
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// //...
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//}
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//
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// running this command
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//func PillString(s string) (Pill, error) {
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// //...
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//}
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//
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// stringer -type=Pill
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//func PillValues() []Pill {
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// //...
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//}
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//
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// in the same directory will create the file pill_string.go, in package painkiller,
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// containing a definition of
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//func (i Pill) IsAPill() bool {
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// //...
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//}
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//
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// func (Pill) String() string
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//func (i Pill) MarshalJSON() ([]byte, error) {
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// //...
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//}
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//
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// That method will translate the value of a Pill constant to the string representation
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// of the respective constant name, so that the call fmt.Print(painkiller.Aspirin) will
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// print the string "Aspirin".
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//func (i *Pill) UnmarshalJSON(data []byte) error {
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// //...
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//}
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//```
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//From now on, we can:
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//```go
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//// Convert any Pill value to string
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//var aspirinString string = Aspirin.String()
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//// (or use it in any place where a Stringer is accepted)
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//fmt.Println("I need ", Paracetamol) // Will print "I need Paracetamol"
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//
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// Typically this process would be run using go generate, like this:
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//// Convert a string with the enum name to the corresponding enum value
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//pill, err := PillString("Ibuprofen")
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//if err != nil {
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// fmt.Println("Unrecognized pill: ", err)
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// return
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//}
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//// Now pill == Ibuprofen
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//
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// //go:generate stringer -type=Pill
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//// Get all the values of the string
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//allPills := PillValues()
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//fmt.Println(allPills) // Will print [Placebo Aspirin Ibuprofen Paracetamol]
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//
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// If multiple constants have the same value, the lexically first matching name will
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// be used (in the example, Acetaminophen will print as "Paracetamol").
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//// Check if a value belongs to the Pill enum values
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//var notAPill Pill = 42
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//if (notAPill.IsAPill()) {
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// fmt.Println(notAPill, "is not a value of the Pill enum")
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//}
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//
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// With no arguments, it processes the package in the current directory.
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// Otherwise, the arguments must name a single directory holding a Go package
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// or a set of Go source files that represent a single Go package.
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//// Marshal/unmarshal to/from json strings, either directly or automatically when
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//// the enum is a field of a struct
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//pillJSON := Aspirin.MarshalJSON()
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//// Now pillJSON == `"Aspirin"`
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//```
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//
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// The -type flag accepts a comma-separated list of types so a single run can
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// generate methods for multiple types. The default output file is t_string.go,
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// where t is the lower-cased name of the first type listed. It can be overridden
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// with the -output flag.
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//The generated code is exactly the same as the Stringer tool plus the mentioned additions, so you can use
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//**Enumer** where you are already using **Stringer** without any code change.
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//
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// ------
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// This is a patched versin of the original stringer. The original generates source code
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// using '_' (underscore) as part of generated golang identifiers. This creates a number of
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// golint warnings. The patched version simply leaves the '_' out
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//## Transforming the string representation of the enum value
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//
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//By default, Enumer uses the same name of the enum value for generating the string representation (usually CamelCase in Go).
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//
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//```go
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//type MyType int
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//
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// ...
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//
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//name := MyTypeValue.String() // name => "MyTypeValue"
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//```
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//
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//Sometimes you need to use some other string representation format than CamelCase (i.e. in JSON).
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//
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//To transform it from CamelCase to snake_case or kebab-case, you can use the `transform` flag.
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//
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//For example, the command `enumer -type=MyType -json -transform=snake` would generate the following string representation:
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//
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//```go
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//name := MyTypeValue.String() // name => "my_type_value"
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//```
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//**Note**: The transformation only works form CamelCase to snake_case or kebab-case, not the other way around.
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//
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//## How to use
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//The usage of Enumer is the same as Stringer, so you can refer to the [Stringer docs](https://godoc.org/golang.org/x/tools/cmd/stringer)
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//for more information.
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//
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//There are four boolean flags: `json`, `text`, `yaml` and `sql`. You can use any combination of them (i.e. `enumer -type=Pill -json -text`),
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//
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//
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//For enum string representation transformation the `transform` and `trimprefix` flags
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//were added (i.e. `enumer -type=MyType -json -transform=snake`).
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//Possible transform values are `snake` and `kebab` for transformation to snake_case and kebab-case accordingly.
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//The default value for `transform` flag is `noop` which means no transformation will be performed.
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//
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//If a prefix is provided via the `trimprefix` flag, it will be trimmed from the start of each name (before
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//it is transformed). If a name doesn't have the prefix it will be passed unchanged.
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//
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//## Inspiring projects
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//* [Stringer](https://godoc.org/golang.org/x/tools/cmd/stringer)
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//* [jsonenums](https://github.com/campoy/jsonenums)
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package main
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import (
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