doylecnn · October 6, 2018 23:57 · Feb 21, 2015 · Feb 21, 2015
diff --git a/README.md b/README.md
@@ -1,5 +1,3 @@
-# Functional Configuration
-
 Quick demo of how to initialize your data structure with optional configuration
 parameters ... with sane defaults if left unspecified.
 

diff --git a/README.md b/README.md
@@ -0,0 +1,13 @@
+# Functional Configuration
+
+Quick demo of how to initialize your data structure with optional configuration
+parameters ... with sane defaults if left unspecified.
+
+This functional config technique ...
+
+* lets you write APIs that can evolve without pain
+* provides meaningful configuration parameters
+* makes it easy to set default settings
+* makes it possible to set complex conditional values
+
+See the posts by Rob Pike (["Self-referential functions and the design of options"](http://commandcenter.blogspot.com.au/2014/01/self-referential-functions-and-design.html)) and Dave Cheney (["Functional options for friendly APIs"](http://dave.cheney.net/2014/10/17/functional-options-for-friendly-apis)) for more details on this technique.
diff --git a/main.go b/main.go
@@ -0,0 +1,30 @@
+package main
+
+import (
+    "fmt"
+    "github.com/joyrexus/person"
+)
+
+func main() {
+
+    bill, _ := person.New("Bill")  // sets defaults for Job, Age, Alive
+
+    fmt.Printf("%#v\n", bill)
+    // {Name:"Bill", Age:0, Job:"unknown", Alive:true}
+
+
+    bob, _ := person.New("Bob", person.Job("programmer"),
+                                person.Age(44))
+
+    fmt.Printf("%#v\n", bob)
+    // {Name:"Bob", Age:44, Job:"programmer", Alive:true}
+
+
+    // change bob's configuration
+    bob.Config(person.Age(33), 
+               person.Job("masseuse"), 
+               person.Alive(false))
+
+    fmt.Printf("%#v\n", bob)
+    // {Name:"Bob", Age:33, Job:"masseuse", Alive:false}
+}
diff --git a/person.go b/person.go
@@ -0,0 +1,54 @@
+package person
+
+import "fmt"
+
+type Person struct{
+    Name string
+    Age int
+    Job string
+    Alive bool
+}
+
+func (p *Person) String() string {
+    return fmt.Sprintf("%s, %v, %s, %v", p.Name, p.Age, p.Job, p.Alive)
+}
+
+type option func(*Person)
+
+// Config sets the options specified.
+func (p *Person) Config(opts ...option) {
+    for _, opt := range opts {
+        opt(p)
+    }
+}
+
+func Age(yrs int) option {
+    return func(p *Person) {
+        p.Age = yrs
+    }
+}
+
+func Job(job string) option {
+    return func(p *Person) {
+        p.Job = job
+    }
+}
+
+func Alive(status bool) option {
+    return func(p *Person) {
+        p.Alive = status
+    }
+}
+
+func New(name string, options ...option) (*Person, error) {
+    p := Person{
+        Name: name,
+        Age: 0,
+        Job: "unknown",
+        Alive: true,
+    }
+    for _, opt := range options {
+        opt(&p)
+    }
+    return &p, nil
+}