A command-line tool to generate a constructor for the struct.
$ go install github.com/moznion/gonstructor/cmd/gonstructor@latest
Also, you can get the pre-built binaries on Releases.
Or get it with gobinaries.com:
curl -sf https://gobinaries.com/moznion/gonstructor | shgonstructor depends on goimports for fixing import paths and formatting code, you need to install it:
$ go install golang.org/x/tools/cmd/goimports@latest
Usage of gonstructor:
-constructorTypes string
[optional] comma-separated list of constructor types; it expects "allArgs" and "builder" (default "allArgs")
-init string
[optional] name of function to call on object after creating it
-output string
[optional] Output file name (default "srcdir/<type>_gen.go"). See also "-type" option's description.'
-propagateInitFuncReturns
[optional] If this option is specified, the generated constructor propagates the return values that come from the init function specified by the "-init" option, e.g. when the init function returns an "error" value, the generated constructor returns (*YourStructType, error). Known issue: If this option is used with the multiple --type options, probably it won't be the expected result.
-type value
[mandatory] A type name. It accepts this option occurs multiple times to output the generated code of the multi types into a single file. If this option is given multiple times, the "-output" option becomes mandatory.
-version
[optional] show the version information
-withGetter
[optional] generate a constructor along with getter functions for each field
Data encapsulation is a good practice to make software, and it is necessary to clearly indicate the boundary of the structure by controlling the accessibility of the data fields (i.e. private or public) for that. Basically keeping the data fields be private and immutable would be good to make software be robust because it can avoid unexpected field changing.
Golang has a simple way to do that by choosing the initial character's type: upper case or lower case. Once it has decided to use a field as private, it needs to make something like a constructor function, but golang doesn't have a mechanism to support constructor now.
Therefore this project aims to automatically generate constructors to use structures with private and immutable, easily.
- write a struct type with
go:generate
e.g.
//go:generate gonstructor --type=Structure --constructorTypes=allArgs
type Structure struct {
foo string
bar io.Reader
Buz chan interface{}
}- execute
go generate ./... - then
gonstructorgenerates a constructor code
e.g.
func NewStructure(foo string, bar io.Reader, buz chan interface{}) *Structure {
return &Structure{foo: foo, bar: bar, Buz: buz}
}- write a struct type with
go:generate
e.g.
//go:generate gonstructor --type=Structure --constructorTypes=builder
type Structure struct {
foo string
bar io.Reader
Buz chan interface{}
}- execute
go generate ./... - then
gonstructorgenerates a buildr code
e.g.
type StructureBuilder struct {
foo string
bar io.Reader
buz chan interface{}
bufferSize int
}
func NewStructureBuilder() *StructureBuilder {
return &StructureBuilder{}
}
func (b *StructureBuilder) Foo(foo string) *StructureBuilder {
b.foo = foo
return b
}
func (b *StructureBuilder) Bar(bar io.Reader) *StructureBuilder {
b.bar = bar
return b
}
func (b *StructureBuilder) Buz(buz chan interface{}) *StructureBuilder {
b.buz = buz
return b
}
func (b *StructureBuilder) BufferSize(bufferSize int) *StructureBuilder {
b.bufferSize = bufferSize
return b
}
func (b *StructureBuilder) Build() *Structure {
return &Structure{
foo: b.foo,
bar: b.bar,
Buz: b.buz,
bufferSize: b.bufferSize,
}
}- write a struct type with
go:generate - write a function that initializes internal fields
- pass its name to
-initparameter
e.g.
//go:generate gonstructor --type=Structure -init construct
type Structure struct {
foo string
bar io.Reader
Buz chan interface{}
bufferSize int
buffer chan []byte `gonstructor:"-"`
}
func (structure *Structure) construct() {
structure.buffer = make(chan []byte, structure.bufferSize)
}- execute
go generate ./... - then
gonstructorgenerates a buildr code
e.g.
func NewStructure(
foo string,
bar io.Reader,
buz chan interface{},
bufferSize int,
) *Structure {
r := &Structure{
foo: foo,
bar: bar,
Buz: buz,
bufferSize: bufferSize,
}
r.construct()
return r
}gonstructor:"-" supports that.
e.g.
type Structure struct {
foo string
bar int64 `gonstructor:"-"`
}The generated code according to the above structure doesn't contain bar field.
This CLI tool can have the --type option multiple times, and it must have also --output option.
example:
//go:generate gonstructor --type=AlphaStructure --type=BravoStructure --constructorTypes=allArgs,builder --withGetter --output=./alpha_and_bravo_gen.go"
-propagateInitFuncReturns option supports that.
For example,
//go:generate gonstructor --type=Struct --constructorTypes=allArgs,builder --init validate --propagateInitFuncReturns
type Struct struct {
foo string
}
func (s *Struct) validate() error {
// do something with the created `Struct` value.
return err
}then it generates the following Go code:
func NewStruct(foo string) (*Struct, error) {
r := &Struct{
foo: foo,
}
ret_validate0 := r.validate()
return r, ret_validate0
}As you can see, the generated constructor NewStruct() returns the constructed value and an error that comes from validate() function.
Binaries are built and uploaded by goreleaser. Please refer to the configuration file: .goreleaser.yml
moznion (moznion@gmail.com)