chapter 11 in progress

learning_go/11_standard_library/README.md

@@ -11,9 +11,45 @@
 ### I/O ops
 * `io.Reader` and `io.Writer` interfaces
 * `io.EOF` error, which is not true error
+* interfaces are safe, type-wise (this weird combination of `duck typing` and `not-duck typing`)
+* `io.Copy`, as name implies, copies data between `io.Reader` and `io.Writer` 
+* `io.Closer` is implemented by `types` like `os.File`, in cases, where you need to clean up something
+* `io.Seeker` enables accesing data in random place of resource
+* cool pattern `ioutil`, shows how to adding method to type, which is not really implementing them, to adhere to some interface (kinda like mocking)
 
+```go
+type nopCloser struct {
+    io.Reader
+}
+
+func (nopCloser) Close() error { return nil}
+
+func NopCloser(r io.Reader) io.ReadCloser {
+    return nopCloser{r}
+}
+```
+
+* but it breaks general rule of `don't return interfaces in functions`
 
 ### Time
+* `time.Duration`
+    * `time.Hour`
+    * `time.Minute`
+    * ...
+    *  nanosec is the smallest one
+* `time.Time`
+    * timezone info is included, so don't compare using `==`, but using `Equals`
+* a little weird format
+
+```go
+t, err := time.Parse("2006-02-01 15:04:05 -0700", "2016-13-03 00:00:00 +0000")
+if err != nil {
+    return err
+}
+fmt.Println(t.Format("January 2, 2006 at 3:04:05PM MST"))
+```
+* now, time in Go guarantees monotonicity (uses monotonic clock, instead of real time)
+* `time.Now()` used to rely on real time, which caused bug described on [cloudflare blog](https://blog.cloudflare.com/how-and-why-the-leap-second-affected-cloudflare-dns/)
 
 ### JSON