optional

package module
v0.2.0 Latest Latest
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 Go to latest Published: Mar 16, 2022 License: MIT Imports: 4 Imported by: 5

README

optional

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go get 4d63.com/optional

import 4d63.com/optional

Package optional exports an Optional[T] type that can wrap any type to represent the lack of value. The types guarantee safety by requiring the developer to unwrap them to get to the inner value. This prevents a nil value being operated on. Optionals marshal to XML and JSON like their underlying type, and omitempty works just like their wrapped type would with a pointer, but without the use of pointers.

These types are an alternative to using pointers, zero values, or similar null wrapper packages. Unlike similar solutions these will omit correctly from XML and JSON without the use of pointers and the compiler will ensure their value is not used when empty.

Examples

Wrap a pointer in an optional:

var i *int = ...
o := optional.OfPtr(i)

Unwrap it safely:

o.If(func(i int) {
	// called if o is not empty
})

if _, ok := o.Get(); ok {
	// ok is true if o is not empty
}

Or get it's value with a fallback to a default:

_ := o.ElseZero() // returns the zero value if empty

_ := o.Else(100) // returns 100 if o is empty

_ := o.ElseFunc(func() {
	// called if o is empty
	return 100
})

XML and JSON are supported out of the box. Use omitempty to omit the field when the optional is empty:

s := struct {
	Int1 optional.Optional[int] `json:"int1,omitempty"`
	Int2 optional.Optional[int] `json:"int2,omitempty"`
	Int3 optional.Optional[int] `json:"int3,omitempty"`
}{
	Int1: optional.Empty[int](),
	Int2: optional.Of(1000),
	Int3: optional.OfPtr(nil),
}

output, _ := json.Marshal(s)

// output = {"int2":1000}
Documentation

See the godoc.

Documentation

Overview

Package optional exports an Optional[T] type that can wrap any type to represent the lack of value. The types guarantee safety by requiring the developer to unwrap them to get to the inner value. This prevents a nil value being operated on. Optionals marshal to XML and JSON like their underlying type, and omitempty works just like their wrapped type would with a pointer, but without the use of pointers.

These types are an alternative to using pointers, zero values, or similar null wrapper packages. Unlike similar solutions these will omit correctly from XML and JSON without the use of pointers and the compiler will ensure their value is not used when empty.

Examples

Wrap a pointer in an optional: 

var i *int = ...
o := optional.OfPtr(i)

Unwrap it safely: 

o.If(func(i int) {
	// called if o is not empty
})

if _, ok := o.Get(); ok {
	// ok is true if o is not empty
}

Or get it's value with a fallback to a default: 

_ := o.ElseZero() // returns the zero value if empty

_ := o.Else(100) // returns 100 if o is empty

_ := o.ElseFunc(func() {
	// called if o is empty
	return 100
})

XML and JSON are supported out of the box. Use `omitempty` to omit the field when the optional is empty: 

s := struct {
	Int1 optional.Optional[int] `json:"int1,omitempty"`
	Int2 optional.Optional[int] `json:"int2,omitempty"`
	Int3 optional.Optional[int] `json:"int3,omitempty"`
}{
	Int1: optional.Empty[int](),
	Int2: optional.Of(1000),
	Int3: optional.OfPtr(nil),
}

output, _ := json.Marshal(s)

// output = {"int2":1000}
Example (Else) 
package main

import (
	"fmt"

	"4d63.com/optional"
)

func main() {
	i := 1001
	values := []optional.Optional[int]{
		optional.Empty[int](),
		optional.Of(1000),
		optional.OfPtr[int](nil),
		optional.OfPtr(&i),
	}

	for _, v := range values {
		fmt.Println(v.Else(1))
	}

}

Output:

1
1000
1
1001
Example (ElseFunc) 
package main

import (
	"fmt"

	"4d63.com/optional"
)

func main() {
	i := 1001
	values := []optional.Optional[int]{
		optional.Empty[int](),
		optional.Of(1000),
		optional.OfPtr[int](nil),
		optional.OfPtr(&i),
	}

	for _, v := range values {
		fmt.Println(v.ElseFunc(func() int {
			return 2
		}))
	}

}

Output:

2
1000
2
1001
Example (ElseZero) 
package main

import (
	"fmt"

	"4d63.com/optional"
)

func main() {
	i := 1001
	values := []optional.Optional[int]{
		optional.Empty[int](),
		optional.Of(1000),
		optional.OfPtr[int](nil),
		optional.OfPtr(&i),
	}

	for _, v := range values {
		fmt.Println(v.ElseZero())
	}

}

Output:

0
1000
0
1001
Example (Get) 
package main

import (
	"fmt"

	"4d63.com/optional"
)

func main() {
	i := 1001
	values := []optional.Optional[int]{
		optional.Empty[int](),
		optional.Of(1000),
		optional.OfPtr[int](nil),
		optional.OfPtr(&i),
	}

	for _, v := range values {
		if i, ok := v.Get(); ok {
			fmt.Println(i)
		}
	}

}

Output:

1000
1001
Example (If) 
package main

import (
	"fmt"

	"4d63.com/optional"
)

func main() {
	i := 1001
	values := []optional.Optional[int]{
		optional.Empty[int](),
		optional.Of(1000),
		optional.OfPtr[int](nil),
		optional.OfPtr(&i),
	}

	for _, v := range values {
		v.If(func(i int) {
			fmt.Println(i)
		})
	}

}

Output:

1000
1001
Example (JsonMarshalEmpty) 
package main

import (
	"encoding/json"
	"fmt"
	"time"

	"4d63.com/optional"
)

func main() {
	s := struct {
		Bool    optional.Optional[bool]      `json:"bool"`
		Byte    optional.Optional[byte]      `json:"byte"`
		Float32 optional.Optional[float32]   `json:"float32"`
		Float64 optional.Optional[float64]   `json:"float64"`
		Int16   optional.Optional[int16]     `json:"int16"`
		Int32   optional.Optional[int32]     `json:"int32"`
		Int64   optional.Optional[int64]     `json:"int64"`
		Int     optional.Optional[int]       `json:"int"`
		Rune    optional.Optional[rune]      `json:"rune"`
		String  optional.Optional[string]    `json:"string"`
		Time    optional.Optional[time.Time] `json:"time"`
		Uint16  optional.Optional[uint16]    `json:"uint16"`
		Uint32  optional.Optional[uint32]    `json:"uint32"`
		Uint64  optional.Optional[uint64]    `json:"uint64"`
		Uint    optional.Optional[uint]      `json:"uint"`
		Uintptr optional.Optional[uintptr]   `json:"uintptr"`
	}{
		Bool:    optional.Empty[bool](),
		Byte:    optional.Empty[byte](),
		Float32: optional.Empty[float32](),
		Float64: optional.Empty[float64](),
		Int16:   optional.Empty[int16](),
		Int32:   optional.Empty[int32](),
		Int64:   optional.Empty[int64](),
		Int:     optional.Empty[int](),
		Rune:    optional.Empty[rune](),
		String:  optional.Empty[string](),
		Time:    optional.Empty[time.Time](),
		Uint16:  optional.Empty[uint16](),
		Uint32:  optional.Empty[uint32](),
		Uint64:  optional.Empty[uint64](),
		Uint:    optional.Empty[uint](),
		Uintptr: optional.Empty[uintptr](),
	}

	output, _ := json.MarshalIndent(s, "", "  ")
	fmt.Println(string(output))

}

Output:

{
  "bool": false,
  "byte": 0,
  "float32": 0,
  "float64": 0,
  "int16": 0,
  "int32": 0,
  "int64": 0,
  "int": 0,
  "rune": 0,
  "string": "",
  "time": "0001-01-01T00:00:00Z",
  "uint16": 0,
  "uint32": 0,
  "uint64": 0,
  "uint": 0,
  "uintptr": 0
}
Example (JsonMarshalOmitEmpty) 
package main

import (
	"encoding/json"
	"fmt"
	"time"

	"4d63.com/optional"
)

func main() {
	s := struct {
		Bool    optional.Optional[bool]      `json:"bool,omitempty"`
		Byte    optional.Optional[byte]      `json:"byte,omitempty"`
		Float32 optional.Optional[float32]   `json:"float32,omitempty"`
		Float64 optional.Optional[float64]   `json:"float64,omitempty"`
		Int16   optional.Optional[int16]     `json:"int16,omitempty"`
		Int32   optional.Optional[int32]     `json:"int32,omitempty"`
		Int64   optional.Optional[int64]     `json:"int64,omitempty"`
		Int     optional.Optional[int]       `json:"int,omitempty"`
		Rune    optional.Optional[rune]      `json:"rune,omitempty"`
		String  optional.Optional[string]    `json:"string,omitempty"`
		Time    optional.Optional[time.Time] `json:"time,omitempty"`
		Uint16  optional.Optional[uint16]    `json:"uint16,omitempty"`
		Uint32  optional.Optional[uint32]    `json:"uint32,omitempty"`
		Uint64  optional.Optional[uint64]    `json:"uint64,omitempty"`
		Uint    optional.Optional[uint]      `json:"uint,omitempty"`
		Uintptr optional.Optional[uintptr]   `json:"uintptr,omitempty"`
	}{
		Bool:    optional.Empty[bool](),
		Byte:    optional.Empty[byte](),
		Float32: optional.Empty[float32](),
		Float64: optional.Empty[float64](),
		Int16:   optional.Empty[int16](),
		Int32:   optional.Empty[int32](),
		Int64:   optional.Empty[int64](),
		Int:     optional.Empty[int](),
		Rune:    optional.Empty[rune](),
		String:  optional.Empty[string](),
		Time:    optional.Empty[time.Time](),
		Uint16:  optional.Empty[uint16](),
		Uint32:  optional.Empty[uint32](),
		Uint64:  optional.Empty[uint64](),
		Uint:    optional.Empty[uint](),
		Uintptr: optional.Empty[uintptr](),
	}

	output, _ := json.MarshalIndent(s, "", "  ")
	fmt.Println(string(output))

}

Output:

{}
Example (JsonMarshalPresent) 
package main

import (
	"encoding/json"
	"fmt"
	"time"

	"4d63.com/optional"
)

func main() {
	s := struct {
		Bool    optional.Optional[bool]      `json:"bool"`
		Byte    optional.Optional[byte]      `json:"byte"`
		Float32 optional.Optional[float32]   `json:"float32"`
		Float64 optional.Optional[float64]   `json:"float64"`
		Int16   optional.Optional[int16]     `json:"int16"`
		Int32   optional.Optional[int32]     `json:"int32"`
		Int64   optional.Optional[int64]     `json:"int64"`
		Int     optional.Optional[int]       `json:"int"`
		Rune    optional.Optional[rune]      `json:"rune"`
		String  optional.Optional[string]    `json:"string"`
		Time    optional.Optional[time.Time] `json:"time"`
		Uint16  optional.Optional[uint16]    `json:"uint16"`
		Uint32  optional.Optional[uint32]    `json:"uint32"`
		Uint64  optional.Optional[uint64]    `json:"uint64"`
		Uint    optional.Optional[uint]      `json:"uint"`
		Uintptr optional.Optional[uintptr]   `json:"uintptr"`
	}{
		Bool:    optional.Of(true),
		Byte:    optional.Of[byte](1),
		Float32: optional.Of[float32](2.1),
		Float64: optional.Of(2.2),
		Int16:   optional.Of[int16](3),
		Int32:   optional.Of[int32](4),
		Int64:   optional.Of[int64](5),
		Int:     optional.Of(6),
		Rune:    optional.Of[rune](7),
		String:  optional.Of("string"),
		Time:    optional.Of(time.Date(2006, 1, 2, 15, 4, 5, 0, time.UTC)),
		Uint16:  optional.Of[uint16](8),
		Uint32:  optional.Of[uint32](9),
		Uint64:  optional.Of[uint64](10),
		Uint:    optional.Of[uint](11),
		Uintptr: optional.Of[uintptr](12),
	}

	output, _ := json.MarshalIndent(s, "", "  ")
	fmt.Println(string(output))

}

Output:

{
  "bool": true,
  "byte": 1,
  "float32": 2.1,
  "float64": 2.2,
  "int16": 3,
  "int32": 4,
  "int64": 5,
  "int": 6,
  "rune": 7,
  "string": "string",
  "time": "2006-01-02T15:04:05Z",
  "uint16": 8,
  "uint32": 9,
  "uint64": 10,
  "uint": 11,
  "uintptr": 12
}
Example (JsonUnmarshalEmpty) 
package main

import (
	"encoding/json"
	"fmt"
	"time"

	"4d63.com/optional"
)

func main() {
	s := struct {
		Bool    optional.Optional[bool]      `json:"bool"`
		Byte    optional.Optional[byte]      `json:"byte"`
		Float32 optional.Optional[float32]   `json:"float32"`
		Float64 optional.Optional[float64]   `json:"float64"`
		Int16   optional.Optional[int16]     `json:"int16"`
		Int32   optional.Optional[int32]     `json:"int32"`
		Int64   optional.Optional[int64]     `json:"int64"`
		Int     optional.Optional[int]       `json:"int"`
		Rune    optional.Optional[rune]      `json:"rune"`
		String  optional.Optional[string]    `json:"string"`
		Time    optional.Optional[time.Time] `json:"time"`
		Uint16  optional.Optional[uint16]    `json:"uint16"`
		Uint32  optional.Optional[uint32]    `json:"uint32"`
		Uint64  optional.Optional[uint64]    `json:"uint64"`
		Uint    optional.Optional[uint]      `json:"uint"`
		Uintptr optional.Optional[uintptr]   `json:"uintptr"`
	}{}

	x := `{}`
	json.Unmarshal([]byte(x), &s)
	fmt.Println("Bool:", s.Bool.IsPresent())
	fmt.Println("Byte:", s.Byte.IsPresent())
	fmt.Println("Float32:", s.Float32.IsPresent())
	fmt.Println("Float64:", s.Float64.IsPresent())
	fmt.Println("Int16:", s.Int16.IsPresent())
	fmt.Println("Int32:", s.Int32.IsPresent())
	fmt.Println("Int64:", s.Int64.IsPresent())
	fmt.Println("Int:", s.Int.IsPresent())
	fmt.Println("Rune:", s.Rune.IsPresent())
	fmt.Println("String:", s.String.IsPresent())
	fmt.Println("Time:", s.Time.IsPresent())
	fmt.Println("Uint16:", s.Uint16.IsPresent())
	fmt.Println("Uint32:", s.Uint32.IsPresent())
	fmt.Println("Uint64:", s.Uint64.IsPresent())
	fmt.Println("Uint64:", s.Uint64.IsPresent())
	fmt.Println("Uint:", s.Uint.IsPresent())
	fmt.Println("Uintptr:", s.Uint.IsPresent())

}

Output:

Bool: false
Byte: false
Float32: false
Float64: false
Int16: false
Int32: false
Int64: false
Int: false
Rune: false
String: false
Time: false
Uint16: false
Uint32: false
Uint64: false
Uint64: false
Uint: false
Uintptr: false
Example (JsonUnmarshalPresent) 
package main

import (
	"encoding/json"
	"fmt"
	"time"

	"4d63.com/optional"
)

func main() {
	s := struct {
		Bool    optional.Optional[bool]      `json:"bool"`
		Byte    optional.Optional[byte]      `json:"byte"`
		Float32 optional.Optional[float32]   `json:"float32"`
		Float64 optional.Optional[float64]   `json:"float64"`
		Int16   optional.Optional[int16]     `json:"int16"`
		Int32   optional.Optional[int32]     `json:"int32"`
		Int64   optional.Optional[int64]     `json:"int64"`
		Int     optional.Optional[int]       `json:"int"`
		Rune    optional.Optional[rune]      `json:"rune"`
		String  optional.Optional[string]    `json:"string"`
		Time    optional.Optional[time.Time] `json:"time"`
		Uint16  optional.Optional[uint16]    `json:"uint16"`
		Uint32  optional.Optional[uint32]    `json:"uint32"`
		Uint64  optional.Optional[uint64]    `json:"uint64"`
		Uint    optional.Optional[uint]      `json:"uint"`
		Uintptr optional.Optional[uintptr]   `json:"uintptr"`
	}{}

	x := `{
   "bool": false,
   "byte": 0,
   "float32": 0,
   "float64": 0,
   "int16": 0,
   "int32": 0,
   "int64": 0,
   "int": 0,
   "rune": 0,
   "string": "string",
   "time": "0001-01-01T00:00:00Z",
   "uint16": 0,
   "uint32": 0,
   "uint64": 0,
   "uint": 0,
   "uintptr": 0
 }`
	json.Unmarshal([]byte(x), &s)
	fmt.Println("Bool:", s.Bool.IsPresent(), s.Bool)
	fmt.Println("Byte:", s.Byte.IsPresent(), s.Byte)
	fmt.Println("Float32:", s.Float32.IsPresent(), s.Float32)
	fmt.Println("Float64:", s.Float64.IsPresent(), s.Float64)
	fmt.Println("Int16:", s.Int16.IsPresent(), s.Int16)
	fmt.Println("Int32:", s.Int32.IsPresent(), s.Int32)
	fmt.Println("Int64:", s.Int64.IsPresent(), s.Int64)
	fmt.Println("Int:", s.Int.IsPresent(), s.Int)
	fmt.Println("Rune:", s.Rune.IsPresent(), s.Rune)
	fmt.Println("String:", s.String.IsPresent(), s.String)
	fmt.Println("Time:", s.Time.IsPresent(), s.Time)
	fmt.Println("Uint16:", s.Uint16.IsPresent(), s.Uint16)
	fmt.Println("Uint32:", s.Uint32.IsPresent(), s.Uint32)
	fmt.Println("Uint64:", s.Uint64.IsPresent(), s.Uint64)
	fmt.Println("Uint64:", s.Uint64.IsPresent(), s.Uint64)
	fmt.Println("Uint:", s.Uint.IsPresent(), s.Uint)
	fmt.Println("Uintptr:", s.Uint.IsPresent(), s.Uint)

}

Output:

Bool: true false
Byte: true 0
Float32: true 0
Float64: true 0
Int16: true 0
Int32: true 0
Int64: true 0
Int: true 0
Rune: true 0
String: true string
Time: true 0001-01-01 00:00:00 +0000 UTC
Uint16: true 0
Uint32: true 0
Uint64: true 0
Uint64: true 0
Uint: true 0
Uintptr: true 0
Example (XmlMarshalEmpty) 
package main

import (
	"encoding/xml"
	"fmt"
	"time"

	"4d63.com/optional"
)

func main() {
	s := struct {
		XMLName xml.Name                     `xml:"s"`
		Bool    optional.Optional[bool]      `xml:"bool"`
		Byte    optional.Optional[byte]      `xml:"byte"`
		Float32 optional.Optional[float32]   `xml:"float32"`
		Float64 optional.Optional[float64]   `xml:"float64"`
		Int16   optional.Optional[int16]     `xml:"int16"`
		Int32   optional.Optional[int32]     `xml:"int32"`
		Int64   optional.Optional[int64]     `xml:"int64"`
		Int     optional.Optional[int]       `xml:"int"`
		Rune    optional.Optional[rune]      `xml:"rune"`
		String  optional.Optional[string]    `xml:"string"`
		Time    optional.Optional[time.Time] `xml:"time"`
		Uint16  optional.Optional[uint16]    `xml:"uint16"`
		Uint32  optional.Optional[uint32]    `xml:"uint32"`
		Uint64  optional.Optional[uint64]    `xml:"uint64"`
		Uint    optional.Optional[uint]      `xml:"uint"`
		Uintptr optional.Optional[uintptr]   `xml:"uintptr"`
	}{
		Bool:    optional.Empty[bool](),
		Byte:    optional.Empty[byte](),
		Float32: optional.Empty[float32](),
		Float64: optional.Empty[float64](),
		Int16:   optional.Empty[int16](),
		Int32:   optional.Empty[int32](),
		Int64:   optional.Empty[int64](),
		Int:     optional.Empty[int](),
		Rune:    optional.Empty[rune](),
		String:  optional.Empty[string](),
		Time:    optional.Empty[time.Time](),
		Uint16:  optional.Empty[uint16](),
		Uint32:  optional.Empty[uint32](),
		Uint64:  optional.Empty[uint64](),
		Uint:    optional.Empty[uint](),
		Uintptr: optional.Empty[uintptr](),
	}

	output, _ := xml.MarshalIndent(s, "", "  ")
	fmt.Println(string(output))

}

Output:

<s>
  <bool>false</bool>
  <byte>0</byte>
  <float32>0</float32>
  <float64>0</float64>
  <int16>0</int16>
  <int32>0</int32>
  <int64>0</int64>
  <int>0</int>
  <rune>0</rune>
  <string></string>
  <time>0001-01-01T00:00:00Z</time>
  <uint16>0</uint16>
  <uint32>0</uint32>
  <uint64>0</uint64>
  <uint>0</uint>
  <uintptr>0</uintptr>
</s>
Example (XmlMarshalOmitEmpty) 
package main

import (
	"encoding/xml"
	"fmt"
	"time"

	"4d63.com/optional"
)

func main() {
	s := struct {
		XMLName xml.Name                     `xml:"s"`
		Bool    optional.Optional[bool]      `xml:"bool,omitempty"`
		Byte    optional.Optional[byte]      `xml:"byte,omitempty"`
		Float32 optional.Optional[float32]   `xml:"float32,omitempty"`
		Float64 optional.Optional[float64]   `xml:"float64,omitempty"`
		Int16   optional.Optional[int16]     `xml:"int16,omitempty"`
		Int32   optional.Optional[int32]     `xml:"int32,omitempty"`
		Int64   optional.Optional[int64]     `xml:"int64,omitempty"`
		Int     optional.Optional[int]       `xml:"int,omitempty"`
		Rune    optional.Optional[rune]      `xml:"rune,omitempty"`
		String  optional.Optional[string]    `xml:"string,omitempty"`
		Time    optional.Optional[time.Time] `xml:"time,omitempty"`
		Uint16  optional.Optional[uint16]    `xml:"uint16,omitempty"`
		Uint32  optional.Optional[uint32]    `xml:"uint32,omitempty"`
		Uint64  optional.Optional[uint64]    `xml:"uint64,omitempty"`
		Uint    optional.Optional[uint]      `xml:"uint,omitempty"`
		Uintptr optional.Optional[uintptr]   `xml:"uintptr,omitempty"`
	}{
		Bool:    optional.Empty[bool](),
		Byte:    optional.Empty[byte](),
		Float32: optional.Empty[float32](),
		Float64: optional.Empty[float64](),
		Int16:   optional.Empty[int16](),
		Int32:   optional.Empty[int32](),
		Int64:   optional.Empty[int64](),
		Int:     optional.Empty[int](),
		Rune:    optional.Empty[rune](),
		String:  optional.Empty[string](),
		Time:    optional.Empty[time.Time](),
		Uint16:  optional.Empty[uint16](),
		Uint32:  optional.Empty[uint32](),
		Uint64:  optional.Empty[uint64](),
		Uint:    optional.Empty[uint](),
		Uintptr: optional.Empty[uintptr](),
	}

	output, _ := xml.MarshalIndent(s, "", "  ")
	fmt.Println(string(output))

}

Output:

<s></s>
Example (XmlMarshalPresent) 
package main

import (
	"encoding/xml"
	"fmt"
	"time"

	"4d63.com/optional"
)

func main() {
	s := struct {
		XMLName xml.Name                     `xml:"s"`
		Bool    optional.Optional[bool]      `xml:"bool"`
		Byte    optional.Optional[byte]      `xml:"byte"`
		Float32 optional.Optional[float32]   `xml:"float32"`
		Float64 optional.Optional[float64]   `xml:"float64"`
		Int16   optional.Optional[int16]     `xml:"int16"`
		Int32   optional.Optional[int32]     `xml:"int32"`
		Int64   optional.Optional[int64]     `xml:"int64"`
		Int     optional.Optional[int]       `xml:"int"`
		Rune    optional.Optional[rune]      `xml:"rune"`
		String  optional.Optional[string]    `xml:"string"`
		Time    optional.Optional[time.Time] `xml:"time"`
		Uint16  optional.Optional[uint16]    `xml:"uint16"`
		Uint32  optional.Optional[uint32]    `xml:"uint32"`
		Uint64  optional.Optional[uint64]    `xml:"uint64"`
		Uint    optional.Optional[uint]      `xml:"uint"`
		Uintptr optional.Optional[uintptr]   `xml:"uintptr"`
	}{
		Bool:    optional.Of(true),
		Byte:    optional.Of[byte](1),
		Float32: optional.Of[float32](2.1),
		Float64: optional.Of(2.2),
		Int16:   optional.Of[int16](3),
		Int32:   optional.Of[int32](4),
		Int64:   optional.Of[int64](5),
		Int:     optional.Of(6),
		Rune:    optional.Of[rune](7),
		String:  optional.Of("string"),
		Time:    optional.Of(time.Date(2006, 1, 2, 15, 4, 5, 0, time.UTC)),
		Uint16:  optional.Of[uint16](8),
		Uint32:  optional.Of[uint32](9),
		Uint64:  optional.Of[uint64](10),
		Uint:    optional.Of[uint](11),
		Uintptr: optional.Of[uintptr](12),
	}

	output, _ := xml.MarshalIndent(s, "", "  ")
	fmt.Println(string(output))

}

Output:

<s>
  <bool>true</bool>
  <byte>1</byte>
  <float32>2.1</float32>
  <float64>2.2</float64>
  <int16>3</int16>
  <int32>4</int32>
  <int64>5</int64>
  <int>6</int>
  <rune>7</rune>
  <string>string</string>
  <time>2006-01-02T15:04:05Z</time>
  <uint16>8</uint16>
  <uint32>9</uint32>
  <uint64>10</uint64>
  <uint>11</uint>
  <uintptr>12</uintptr>
</s>
Example (XmlUnmarshalEmpty) 
package main

import (
	"encoding/xml"
	"fmt"
	"time"

	"4d63.com/optional"
)

func main() {
	s := struct {
		XMLName xml.Name                     `xml:"s"`
		Bool    optional.Optional[bool]      `xml:"bool"`
		Byte    optional.Optional[byte]      `xml:"byte"`
		Float32 optional.Optional[float32]   `xml:"float32"`
		Float64 optional.Optional[float64]   `xml:"float64"`
		Int16   optional.Optional[int16]     `xml:"int16"`
		Int32   optional.Optional[int32]     `xml:"int32"`
		Int64   optional.Optional[int64]     `xml:"int64"`
		Int     optional.Optional[int]       `xml:"int"`
		Rune    optional.Optional[rune]      `xml:"rune"`
		String  optional.Optional[string]    `xml:"string"`
		Time    optional.Optional[time.Time] `xml:"time"`
		Uint16  optional.Optional[uint16]    `xml:"uint16"`
		Uint32  optional.Optional[uint32]    `xml:"uint32"`
		Uint64  optional.Optional[uint64]    `xml:"uint64"`
		Uint    optional.Optional[uint]      `xml:"uint"`
		Uintptr optional.Optional[uintptr]   `xml:"uintptr"`
	}{}

	x := `<s></s>`
	xml.Unmarshal([]byte(x), &s)
	fmt.Println("Bool:", s.Bool.IsPresent())
	fmt.Println("Byte:", s.Byte.IsPresent())
	fmt.Println("Float32:", s.Float32.IsPresent())
	fmt.Println("Float64:", s.Float64.IsPresent())
	fmt.Println("Int16:", s.Int16.IsPresent())
	fmt.Println("Int32:", s.Int32.IsPresent())
	fmt.Println("Int64:", s.Int64.IsPresent())
	fmt.Println("Int:", s.Int.IsPresent())
	fmt.Println("Rune:", s.Rune.IsPresent())
	fmt.Println("String:", s.String.IsPresent())
	fmt.Println("Time:", s.Time.IsPresent())
	fmt.Println("Uint16:", s.Uint16.IsPresent())
	fmt.Println("Uint32:", s.Uint32.IsPresent())
	fmt.Println("Uint64:", s.Uint64.IsPresent())
	fmt.Println("Uint64:", s.Uint64.IsPresent())
	fmt.Println("Uint:", s.Uint.IsPresent())
	fmt.Println("Uintptr:", s.Uint.IsPresent())

}

Output:

Bool: false
Byte: false
Float32: false
Float64: false
Int16: false
Int32: false
Int64: false
Int: false
Rune: false
String: false
Time: false
Uint16: false
Uint32: false
Uint64: false
Uint64: false
Uint: false
Uintptr: false
Example (XmlUnmarshalPresent) 
package main

import (
	"encoding/xml"
	"fmt"
	"time"

	"4d63.com/optional"
)

func main() {
	s := struct {
		XMLName xml.Name                     `xml:"s"`
		Bool    optional.Optional[bool]      `xml:"bool"`
		Byte    optional.Optional[byte]      `xml:"byte"`
		Float32 optional.Optional[float32]   `xml:"float32"`
		Float64 optional.Optional[float64]   `xml:"float64"`
		Int16   optional.Optional[int16]     `xml:"int16"`
		Int32   optional.Optional[int32]     `xml:"int32"`
		Int64   optional.Optional[int64]     `xml:"int64"`
		Int     optional.Optional[int]       `xml:"int"`
		Rune    optional.Optional[rune]      `xml:"rune"`
		String  optional.Optional[string]    `xml:"string"`
		Time    optional.Optional[time.Time] `xml:"time"`
		Uint16  optional.Optional[uint16]    `xml:"uint16"`
		Uint32  optional.Optional[uint32]    `xml:"uint32"`
		Uint64  optional.Optional[uint64]    `xml:"uint64"`
		Uint    optional.Optional[uint]      `xml:"uint"`
		Uintptr optional.Optional[uintptr]   `xml:"uintptr"`
	}{}

	x := `<s>
   <bool>false</bool>
   <byte>0</byte>
   <float32>0</float32>
   <float64>0</float64>
   <int16>0</int16>
   <int32>0</int32>
   <int64>0</int64>
   <int>0</int>
   <rune>0</rune>
   <string>string</string>
   <time>0001-01-01T00:00:00Z</time>
   <uint16>0</uint16>
   <uint32>0</uint32>
   <uint64>0</uint64>
   <uint>0</uint>
   <uintptr>0</uintptr>
 </s>`
	xml.Unmarshal([]byte(x), &s)
	fmt.Println("Bool:", s.Bool.IsPresent(), s.Bool)
	fmt.Println("Byte:", s.Byte.IsPresent(), s.Byte)
	fmt.Println("Float32:", s.Float32.IsPresent(), s.Float32)
	fmt.Println("Float64:", s.Float64.IsPresent(), s.Float64)
	fmt.Println("Int16:", s.Int16.IsPresent(), s.Int16)
	fmt.Println("Int32:", s.Int32.IsPresent(), s.Int32)
	fmt.Println("Int64:", s.Int64.IsPresent(), s.Int64)
	fmt.Println("Int:", s.Int.IsPresent(), s.Int)
	fmt.Println("Rune:", s.Rune.IsPresent(), s.Rune)
	fmt.Println("String:", s.String.IsPresent(), s.String)
	fmt.Println("Time:", s.Time.IsPresent(), s.Time)
	fmt.Println("Uint16:", s.Uint16.IsPresent(), s.Uint16)
	fmt.Println("Uint32:", s.Uint32.IsPresent(), s.Uint32)
	fmt.Println("Uint64:", s.Uint64.IsPresent(), s.Uint64)
	fmt.Println("Uint64:", s.Uint64.IsPresent(), s.Uint64)
	fmt.Println("Uint:", s.Uint.IsPresent(), s.Uint)
	fmt.Println("Uintptr:", s.Uint.IsPresent(), s.Uint)

}

Output:

Bool: true false
Byte: true 0
Float32: true 0
Float64: true 0
Int16: true 0
Int32: true 0
Int64: true 0
Int: true 0
Rune: true 0
String: true string
Time: true 0001-01-01 00:00:00 +0000 UTC
Uint16: true 0
Uint32: true 0
Uint64: true 0
Uint64: true 0
Uint: true 0
Uintptr: true 0

Index

Examples

Constants

This section is empty.

Variables

This section is empty.

Functions

This section is empty.

Types

type Optional added in v0.2.0 

type Optional[T any] optional[T]

func Empty added in v0.2.0 

func Empty[T any]() Optional[T]

Empty returns an empty optional.

func Of added in v0.2.0 

func Of[T any](value T) Optional[T]

Of wraps the value in an optional.

func OfPtr added in v0.2.0 

func OfPtr[T any](ptr *T) Optional[T]

func (Optional[T]) Else added in v0.2.0 

func (o Optional[T]) Else(elseValue T) (value T)

Else returns the value wrapped by this optional, or the value passed in if there is no value wrapped by this optional.

func (Optional[T]) ElseFunc added in v0.2.0 

func (o Optional[T]) ElseFunc(f func() T) (value T)

func (Optional[T]) ElseZero added in v0.2.0 

func (o Optional[T]) ElseZero() (value T)

ElseZero returns the value wrapped by this optional, or the zero value of the type wrapped if there is no value wrapped by this optional.

func (Optional[T]) Get added in v0.2.0 

func (o Optional[T]) Get() (value T, ok bool)

Get returns the value wrapped by this optional, and an ok signal for whether a value was wrapped.

func (Optional[T]) If added in v0.2.0 

func (o Optional[T]) If(f func(value T))

If calls the function if there is a value wrapped by this optional.

func (Optional[T]) IsPresent added in v0.2.0 

func (o Optional[T]) IsPresent() bool

IsPresent returns true if there is a value wrapped by this optional.

func (Optional[T]) MarshalJSON added in v0.2.0 

func (o Optional[T]) MarshalJSON() (data []byte, err error)

MarshalJSON marshals the value being wrapped to JSON. If there is no vale being wrapped, the zero value of its type is marshaled.

func (Optional[T]) MarshalXML added in v0.2.0 

func (o Optional[T]) MarshalXML(e *xml.Encoder, start xml.StartElement) error

MarshalXML marshals the value being wrapped to XML. If there is no vale being wrapped, the zero value of its type is marshaled.

func (Optional[T]) String added in v0.2.0 

func (o Optional[T]) String() string

String returns the string representation of the wrapped value, or the string representation of the zero value of the type wrapped if there is no value wrapped by this optional.

func (*Optional[T]) UnmarshalJSON added in v0.2.0 

func (o *Optional[T]) UnmarshalJSON(data []byte) error

UnmarshalJSON unmarshals the JSON into a value wrapped by this optional.

func (*Optional[T]) UnmarshalXML added in v0.2.0 

func (o *Optional[T]) UnmarshalXML(d *xml.Decoder, start xml.StartElement) error

UnmarshalXML unmarshals the XML into a value wrapped by this optional.

Source Files

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