commit b985c9ff0bfb1f050d425715a941a51e35f5d0c4
Author: jolheiser <john.olheiser@gmail.com>
Date:   Thu Mar 3 14:50:36 2022 -0600

    Initial commit
    
    Signed-off-by: jolheiser <john.olheiser@gmail.com>

diff --git a/.gitignore b/.gitignore
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--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+.idea/
\ No newline at end of file
diff --git a/LICENSE b/LICENSE
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--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,19 @@
+Copyright (c) 2022 John Olheiser
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/README.md b/README.md
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--- /dev/null
+++ b/README.md
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+# opt
+
+`opt` is a tiny package that reduces boilerplate for functional options.
+
+Simply decide whether your options can return errors or not, then use the corresponding type.
+
+Without errors:
+```go
+type Foo struct {
+	Bar string
+}
+
+func WithBar(b string) opt.Func[Foo] {
+	return func(f *Foo) {
+		f.Bar = b
+    }
+}
+```
+
+With errors:
+```go
+type Foo struct {
+	Bar string
+}
+
+func WithBar(b string) opt.ErrorFunc[Foo] {
+	return func(f *Foo) error  {
+		f.Bar = b
+		return nil
+    }
+}
+```
+
+## License
+
+[MIT](LICENSE)
+
+Credit to `@segfaultax` in the [Discord Gophers](https://discord.gg/golang) server for the idea and starting implementation.
\ No newline at end of file
diff --git a/go.mod b/go.mod
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--- /dev/null
+++ b/go.mod
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+module go.jolheiser.com/opt
+
+go 1.18
+
+require github.com/matryer/is v1.4.0
diff --git a/go.sum b/go.sum
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--- /dev/null
+++ b/go.sum
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+github.com/matryer/is v1.4.0 h1:sosSmIWwkYITGrxZ25ULNDeKiMNzFSr4V/eqBQP0PeE=
+github.com/matryer/is v1.4.0/go.mod h1:8I/i5uYgLzgsgEloJE1U6xx5HkBQpAZvepWuujKwMRU=
diff --git a/opt.go b/opt.go
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--- /dev/null
+++ b/opt.go
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+package opt
+
+// Func is a functional option for A
+type Func[A any] func(*A)
+
+// Apply applies all options to A
+func Apply[A any](a *A, opts ...Func[A]) {
+	for _, opt := range opts {
+		opt(a)
+	}
+}
+
+// ErrorFunc is a functional option for A that can return an error
+type ErrorFunc[A any] func(*A) error
+
+// ApplyError applies all options to A, returning the first error
+func ApplyError[A any](a *A, opts ...ErrorFunc[A]) error {
+	for _, opt := range opts {
+		if err := opt(a); err != nil {
+			return err
+		}
+	}
+	return nil
+}
diff --git a/opt_example_test.go b/opt_example_test.go
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index 0000000..b7fead9
--- /dev/null
+++ b/opt_example_test.go
@@ -0,0 +1,30 @@
+package opt_test
+
+import (
+	"fmt"
+
+	"go.jolheiser.com/opt"
+)
+
+func ExampleApply() {
+	f := &Foo{
+		Bar: "default",
+	}
+	opt.Apply(f, WithBar("override"))
+
+	fmt.Println(f.Bar)
+	// Output:
+	// override
+}
+
+func ExampleApplyError() {
+	f := &Foo{
+		Bar: "default",
+	}
+	err := opt.ApplyError(f, WithBarErr("uh oh!")) // WithBarErr always returns errors.New(b)
+	if err != nil {
+		fmt.Println(err)
+	}
+	// Output:
+	// uh oh!
+}
diff --git a/opt_test.go b/opt_test.go
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index 0000000..21a93c8
--- /dev/null
+++ b/opt_test.go
@@ -0,0 +1,69 @@
+package opt_test
+
+import (
+	"errors"
+	"strconv"
+	"testing"
+
+	"go.jolheiser.com/opt"
+
+	"github.com/matryer/is"
+)
+
+func TestOptions(t *testing.T) {
+	assert := is.New(t)
+
+	f := NewFoo(WithBar("bar"))
+	assert.Equal(f.Bar, "bar") // Option should set bar
+
+	opt.Apply(f, WithBaz(100))
+	assert.Equal(f.Baz, 100) // Apply should set Baz
+
+	_, err := NewErrorFoo(WithBarErr("bar"))
+	assert.True(err != nil)          // ErrorOption should return error
+	assert.Equal(err.Error(), "bar") // ErrorOption error should be bar
+
+	err = opt.ApplyError(f, WithBazErr(100))
+	assert.True(err != nil)          // ApplyError should return error
+	assert.Equal(err.Error(), "100") // ApplyError error should be 100
+}
+
+type Foo struct {
+	Bar string
+	Baz int
+}
+
+func WithBar(b string) opt.Func[Foo] {
+	return func(f *Foo) {
+		f.Bar = b
+	}
+}
+
+func WithBaz(b int) opt.Func[Foo] {
+	return func(f *Foo) {
+		f.Baz = b
+	}
+}
+
+func NewFoo(opts ...opt.Func[Foo]) *Foo {
+	f := &Foo{ /** some defaults **/ }
+	opt.Apply(f, opts...)
+	return f
+}
+
+func NewErrorFoo(opts ...opt.ErrorFunc[Foo]) (*Foo, error) {
+	f := &Foo{ /** some defaults **/ }
+	return f, opt.ApplyError(f, opts...)
+}
+
+func WithBarErr(b string) opt.ErrorFunc[Foo] {
+	return func(f *Foo) error {
+		return errors.New(b)
+	}
+}
+
+func WithBazErr(b int) opt.ErrorFunc[Foo] {
+	return func(f *Foo) error {
+		return errors.New(strconv.Itoa(b))
+	}
+}