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Merge pull request #5 from go-andiamo/clear-and-set
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@marrow16
marrow16 authored Nov 12, 2022
2 parents 18deeb0 + 1e58098 commit 996ffcb
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182 changes: 182 additions & 0 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -37,6 +37,62 @@ func main() {
println(opt2.OrElse(-1))
}
```
[try on go-playground](https://go.dev/play/p/U0dKTrGlG-e)

Optionals can also be very useful when used in conjunction with JSON unmarshalling - to determine whether unmarshalled properties were actually present, with a valid value, in the JSON. The following code demonstrates...
```go
package main

import (
"encoding/json"
"fmt"
. "github.com/go-andiamo/gopt"
)

type NormalStruct struct {
Foo string
Bar int
Baz float64
}

type OptsStruct struct {
Foo Optional[string]
Bar Optional[int]
Baz Optional[float64]
}

func main() {
jdata := `{"Foo": null, "Bar": 1}`

normal := &NormalStruct{}
err := json.Unmarshal([]byte(jdata), normal)
if err == nil {
// was property Foo set???
fmt.Printf("'Foo` was set to \"%s\"???\n", normal.Foo) // was it really?
// was property Bar actually set to 0???
fmt.Printf("'Bar` was set to \"%d\"???\n", normal.Bar) // was it really?
// was property Baz actually set to 0???
fmt.Printf("'Baz` was set to \"%f\"???\n", normal.Baz) // was it really?
} else {
println(err.Error())
}

println()
// now try with optionals...
opts := &OptsStruct{}
err = json.Unmarshal([]byte(jdata), opts)
if err == nil {
fmt.Printf("'Foo` was set - %t\n", opts.Foo.WasSet())
fmt.Printf("'Foo` had valid value - %t\n", opts.Foo.IsPresent())
fmt.Printf("'Bar` was set - %t\n", opts.Bar.WasSet())
fmt.Printf("'Bar` had valid value - %t\n", opts.Bar.IsPresent())
fmt.Printf("'Baz` was set - %t\n", opts.Baz.WasSet())
fmt.Printf("'Baz` had valid value - %t\n", opts.Baz.IsPresent())
} else {
println(err.Error())
}
}
```

## Methods
<table>
Expand Down Expand Up @@ -65,6 +121,15 @@ func main() {
</td>
<td><code>bool</code></td>
</tr>
<tr>
<td>
<code>WasSet()</code><br>
returns true if the last setting operation set the value, otherwise false<br>
Setting operations are <code>UnmarshalJSON()</code>, <code>Scan()</code> and <code>OrElseSet()</code><br>
Use method <code>UnSet()</code> to clear this flag alone
</td>
<td><code>bool</code></td>
</tr>
<tr>
<td>
<code>IfPresent(f func(v T))</code><br>
Expand Down Expand Up @@ -159,6 +224,21 @@ func main() {
</td>
<td><code>error</code></td>
</tr>
<tr>
<td>
<code>Clear()</code><br>
clears the optional<br>
Clearing sets the present to false, the set flag to false and the value to an empty value
</td>
<td><code>Optional[T]</code></td>
</tr>
<tr>
<td>
<code>UnSet()</code><br>
clears the set flag (see <code>WasSet()</code>)
</td>
<td><code>Optional[T]</code></td>
</tr>
</table>

## Constructors
Expand Down Expand Up @@ -192,4 +272,106 @@ func main() {
Creates a new empty (not-present) optional of the specified type
</td>
</tr>
<tr>
<td>
<code>EmptyString() Optional[string]</code><br>
returns an empty optional of type <code>string</code>
</td>
</tr>
<tr>
<td>
<code>EmptyInterface() Optional[interface{}]</code><br>
returns an empty optional of type <code>interface{}</code>
</td>
</tr>
<tr>
<td>
<code>EmptyInt() Optional[int]</code><br>
returns an empty optional of type <code>int</code>
</td>
</tr>
<tr>
<td>
<code>EmptyInt8() Optional[int8]</code><br>
7 returns an empty optional of type <code>int8</code>
</td>
</tr>
<tr>
<td>
<code>EmptyInt16() Optional[int16]</code><br>
returns an empty optional of type <code>int16</code>
</td>
</tr>
<tr>
<td>
<code>EmptyInt32() Optional[int32]</code><br>
returns an empty optional of type <code>int32</code>
</td>
</tr>
<tr>
<td>
<code>EmptyInt64() Optional[int64]</code><br>
returns an empty optional of type <code>int64</code>
</td>
</tr>
<tr>
<td>
<code>EmptyUint() Optional[uint]</code><br>
returns an empty optional of type <code>uint</code>
</td>
</tr>
<tr>
<td>
<code>EmptyUint8() Optional[uint8]</code><br>
returns an empty optional of type <code>uint8</code>
</td>
</tr>
<tr>
<td>
<code>EmptyUint16() Optional[uint16]</code><br>
returns an empty optional of type <code>uint16</code>
</td>
</tr>
<tr>
<td>
<code>EmptyUint32() Optional[uint32]</code><br>
returns an empty optional of type <code>uint32</code>
</td>
</tr>
<tr>
<td>
<code>func EmptyUint64() Optional[uint64]</code><br>
returns an empty optional of type <code>uint64</code>
</td>
</tr>
<tr>
<td>
<code>EmptyBool() Optional[bool]</code><br>
returns an empty optional of type <code>bool</code>
</td>
</tr>
<tr>
<td>
<code>EmptyFloat32() Optional[float32]</code><br>
returns an empty optional of type <code>float32</code>
</td>
</tr>
<tr>
<td>
<code>EmptyFloat64() Optional[float64]</code><br>
returns an empty optional of type <code>float64</code>
</td>
</tr>
<tr>
<td>
<code>EmptyByte() Optional[byte]</code><br>
returns an empty optional of type <code>byte</code>
</td>
</tr>
<tr>
<td>
<code>EmptyRune() Optional[rune]</code><br>
returns an empty optional of type <code>rune</code>
</td>
</tr>
</table>
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