A library that provides Go Generics friendly "optional" features.

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A library that provides Go Generics friendly "optional" features.

Synopsis

true fmt.Printf("%v\n", some.IsNone()) // => false v, err := some.Take() fmt.Printf("err is nil: %v\n", err == nil) // => err is nil: true fmt.Printf("%d\n", v) // => 123 mapped := optional.Map(some, func (v int) int { return v * 2 }) fmt.Printf("%v\n", mapped.IsSome()) // => true mappedValue, _ := some.Take() fmt.Printf("%d\n", mappedValue) // => 246 ">
some := optional.Some[int](123)
fmt.Printf("%v\n", some.IsSome()) // => true
fmt.Printf("%v\n", some.IsNone()) // => false

v, err := some.Take()
fmt.Printf("err is nil: %v\n", err == nil) // => err is nil: true
fmt.Printf("%d\n", v) // => 123

mapped := optional.Map(some, func (v int) int {
    return v * 2
})
fmt.Printf("%v\n", mapped.IsSome()) // => true

mappedValue, _ := some.Take()
fmt.Printf("%d\n", mappedValue) // => 246
false fmt.Printf("%v\n", none.IsNone()) // => true _, err := none.Take() fmt.Printf("err is nil: %v\n", err == nil) // => err is nil: false // the error must be `ErrNoneValueTaken` mapped := optional.Map(none, func (v int) int { return v * 2 }) fmt.Printf("%v\n", mapped.IsNone()) // => true ">
none := optional.None[int]()
fmt.Printf("%v\n", none.IsSome()) // => false
fmt.Printf("%v\n", none.IsNone()) // => true

_, err := none.Take()
fmt.Printf("err is nil: %v\n", err == nil) // => err is nil: false
// the error must be `ErrNoneValueTaken`

mapped := optional.Map(none, func (v int) int {
    return v * 2
})
fmt.Printf("%v\n", mapped.IsNone()) // => true

and more detailed examples are here.

Docs

GoDoc

Tips

  • it would be better to deal with an Option value as a non-pointer because if the Option value can accept nil it becomes worthless

Current Status

Currently (at the moment: Nov 18, 2021), go 1.18 has not been released yet, so if you'd like to try this, please use the tip runtime.
Of course, the new runtime version hasn't been released yet so this library has the possibility to change the implementation as well.

Known Issues

The runtime raises a compile error like "methods cannot have type parameters", so Map(), MapOr(), Zip() and ZipWith() has been providing as functions. Basically, it would be better to provide them as the methods, but currently, it compromises with the limitation.

Author

moznion ([email protected])

Owner
moznion
I usually don't read e-mail. If you want to tell me something (e.g. "response an issue just now!"), please send me a message through twitter:@moznion.
moznion
Comments
  • Support `OrElse`

    Support `OrElse`

    Simple usecase:

    optionalResult := db.call()
    
    
    # as-is
    optionalResult.IfNone(func() {
      optionalResult = db.someOtherCall()
    }
    return optionalResult
    
    
    # to-be
    return optionalResult.OrElse(db.someOtherCall)
    

    rust's Option supports this: https://doc.rust-lang.org/std/option/enum.Option.html#method.or_else

    Thanks for your work!

  • Support `#OrElse()` that supports to return the `Option` value according to the actual value existence

    Support `#OrElse()` that supports to return the `Option` value according to the actual value existence

    Usage example is here: https://github.com/moznion/go-optional/pull/21/files#diff-533b7626d1981e5b4f6500e692dfffc48f5cfd3d078c24bf831abbeb4bf5fccc Close #20

  • Update module github.com/stretchr/testify to v1.8.1

    Update module github.com/stretchr/testify to v1.8.1

    Mend Renovate

    This PR contains the following updates:

    | Package | Type | Update | Change | |---|---|---|---| | github.com/stretchr/testify | require | patch | v1.8.0 -> v1.8.1 |


    Release Notes

    stretchr/testify

    v1.8.1

    Compare Source


    Configuration

    📅 Schedule: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

    🚦 Automerge: Disabled by config. Please merge this manually once you are satisfied.

    ♻ Rebasing: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

    🔕 Ignore: Close this PR and you won't be reminded about this update again.


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  • Update module github.com/stretchr/testify to v1.8.0

    Update module github.com/stretchr/testify to v1.8.0

    Mend Renovate

    This PR contains the following updates:

    | Package | Type | Update | Change | |---|---|---|---| | github.com/stretchr/testify | require | minor | v1.7.2 -> v1.8.0 |


    Release Notes

    stretchr/testify

    v1.8.0

    Compare Source

    v1.7.5

    Compare Source

    v1.7.4

    Compare Source

    v1.7.3

    Compare Source


    Configuration

    📅 Schedule: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

    🚦 Automerge: Disabled by config. Please merge this manually once you are satisfied.

    ♻ Rebasing: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

    🔕 Ignore: Close this PR and you won't be reminded about this update again.


    • [ ] If you want to rebase/retry this PR, click this checkbox.

    This PR has been generated by Mend Renovate. View repository job log here.

  • Update module github.com/stretchr/testify to v1.7.1

    Update module github.com/stretchr/testify to v1.7.1

    WhiteSource Renovate

    This PR contains the following updates:

    | Package | Type | Update | Change | |---|---|---|---| | github.com/stretchr/testify | require | patch | v1.7.0 -> v1.7.1 |


    Release Notes

    stretchr/testify

    v1.7.1

    Compare Source


    Configuration

    📅 Schedule: At any time (no schedule defined).

    🚦 Automerge: Disabled by config. Please merge this manually once you are satisfied.

    ♻ Rebasing: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

    🔕 Ignore: Close this PR and you won't be reminded about this update again.


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  • Support two value factory methods: `FromNillable()` and `PtrFromNillable()`

    Support two value factory methods: `FromNillable()` and `PtrFromNillable()`

    These methods accept the nillable pointer value as an argument and make the Optional[T] type value.

    FromNillable()

    If the given value is not nil, this returns Some[T] value with doing value-dereference. On the other hand, if the value is nil, this returns None[T].

    example:

    num := 123
    
    some := FromNillable[int](&num)
    fmt.Printf("%v\n", some.IsSome()) // => true
    fmt.Printf("%v\n", some.Unwrap()) // => 123
    
    none := FromNillable[int](nil)
    fmt.Printf("%v\n", none.IsSome()) // => false
    fmt.Printf("%v\n", none.Unwrap()) // => 0 (the default value of int)
    

    PtrFromNillable()

    If the given value is not nil, this returns Some[*T] value without doing value-dereference. On the other hand, if the value is nil, this returns None[*T].

    example:

    num := 123
    
    some := PtrFromNillable[int](&num)
    fmt.Printf("%v\n", some.IsSome())  // => true
    fmt.Printf("%v\n", *some.Unwrap()) // => 123 (NOTE: it needs doing dereference)
    
    none := PtrFromNillable[int](nil)
    fmt.Printf("%v\n", none.IsSome()) // => false
    fmt.Printf("%v\n", none.Unwrap()) // => nil
    
  • Support `omitempty` option on JSON marshaling

    Support `omitempty` option on JSON marshaling

    This pull request makes it support the omitempty option on JSON marshaling. If the property has that option and the value is None[T], it omits that property from serialized JSON string.

    example:

    type JSONStruct struct {
    	OmitemptyVal Option[string] `json:"omitemptyVal,omitempty"` // this should be omitted
    }
    jsonStruct := &JSONStruct{OmitemptyVal: None[string]()}
    marshal, err := json.Marshal(jsonStruct)
    if err != nil {
    	return err
    }
    fmt.Printf("%s\n", marshal) // => {}
    
  • Update module go to 1.19

    Update module go to 1.19

    Mend Renovate

    This PR contains the following updates:

    | Package | Type | Update | Change | |---|---|---|---| | go (source) | golang | minor | 1.18 -> 1.19 |


    Release Notes

    golang/go

    v1.19.0


    Configuration

    📅 Schedule: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

    🚦 Automerge: Disabled by config. Please merge this manually once you are satisfied.

    ♻ Rebasing: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

    🔕 Ignore: Close this PR and you won't be reminded about this update again.


    • [ ] If you want to rebase/retry this PR, click this checkbox.

    This PR has been generated by Mend Renovate. View repository job log here.

  • Support `FlatMap` functions:

    Support `FlatMap` functions:

    • FlatMap[T, U any](option Option[T], mapper func(v T) Option[U]) Option[U]
    • FlatMapOr[T, U any](option Option[T], fallbackValue U, mapper func(v T) Option[U]) U
    • FlatMapWithError[T, U any](option Option[T], mapper func(v T) (Option[U], error)) (Option[U], error)
    • FlatMapOrWithError[T, U any](option Option[T], fallbackValue U, mapper func(v T) (Option[U], error)) (U, error)
  • Support Option[T]#Unwrap() method

    Support Option[T]#Unwrap() method

    Unwrap returns the value regardless of Some/None status. If the Option value is Some, this method returns the actual value. On the other hand, if the Option value is None, this method returns the default value according to the type.

  • Add new `If*` method onto Option struct

    Add new `If*` method onto Option struct

    • func (o Option[T]) IfSome(f func(v T))
    • func (o Option[T]) IfSomeWithError(f func(v T) error) error
    • func (o Option[T]) IfNone(f func())
    • func (o Option[T]) IfNoneWithError(f func() error) erro
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    Detected dependencies

    github-actions
    .github/workflows/check.yml
    • actions/setup-go v3
    • actions/checkout v3
    • golangci/golangci-lint-action v3
    • codecov/codecov-action v2
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    • go 1.19
    • github.com/stretchr/testify v1.8.1

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