creational/object-pool: reimplement the object pool pattern

Author: tmrts

README.md

@@ -18,7 +18,7 @@ A curated collection of idiomatic design & application patterns for Go language.
 | [Abstract Factory](/creational/abstract_factory.md) | Provides an interface for creating families of releated objects | ✘ |
 | [Builder](/creational/builder.md) | Builds a complex object using simple objects | ✘ |
 | [Factory Method](/creational/factory.md) | Defers instantiation of an object to a specialized function for creating instances | ✘ |
-| [Object Pool](/creational/object_pool.md) | Instantiates and maintains a group of objects instances of the same type | ✔ |
+| [Object Pool](/creational/object-pool.md) | Instantiates and maintains a group of objects instances of the same type | ✔ |
 | [Singleton](/creational/singleton.md) | Restricts instantiation of a type to one object | ✔ |
 
 ## Structural Patterns

SUMMARY.md

@@ -5,7 +5,7 @@
     * [Abstract Factory](/creational/abstract_factory.md)
     * [Builder](/creational/builder.md)
     * [Factory Method](/creational/factory.md)
-    * [Object Pool](/creational/object_pool.md)
+    * [Object Pool](/creational/object-pool.md)
     * [Singleton](/creational/singleton.md)
   * [Structural Patterns](/README.md#structural-patterns)
     * [Adapter](/structural/adapter.md)

creational/object-pool.md

@@ -0,0 +1,48 @@
+# Object Pool Pattern
+
+The object pool creational design pattern is used to prepare and keep multiple
+instances according to the demand expectation.
+
+## Implementation
+
+```go
+package pool
+
+type Pool chan *Object
+
+func New(total int) *Pool {
+	p := make(chan *Object, total)
+
+	for i := 0; i < total; i++ {
+		p <- new(Object)
+	}
+
+	return p
+}
+```
+
+## Usage
+
+Given below is a simple lifecycle example on an object pool.
+
+```go
+p := pool.New(2)
+
+select {
+case obj := <-p:
+	obj.Do( /*...*/ )
+
+	p <- obj
+default:
+	// No more objects left retry later or fail
+	return
+}
+```
+
+## Rules of Thumb
+
+- Object pool pattern is useful in cases where object initialization is more
+  expensive than the object maintenance.
+- If there are spikes in demand as opposed to a steady demand, the maintenance
+  overhead might overweigh the benefits of an object pool.
+- It has positive effects on performance due to object being initialized beforehand.