Tweak interface example type assertion + update link

Author: eliben

examples/interfaces/interfaces.go

@@ -51,12 +51,12 @@ func measure(g geometry) {
 	fmt.Println(g.perim())
 }
 
-// Type assertion can be performed to explicitly check the runtime type of the value.
-// It allows the access of fields and methods belonging to the specific type.
-// See [`switch` example](switch) for an alternative approach to handle type assertion.
+// Sometimes it's useful to know the runtime type of an
+// interface value. One option is using a *type assertion*
+// as shown here; another is a [type `switch`](switch).
 func detectCircle(g geometry) {
 	if c, ok := g.(circle); ok {
-		fmt.Println(c.radius)
+		fmt.Println("circle with radius", c.radius)
 	}
 }
 
@@ -71,9 +71,6 @@ func main() {
 	measure(r)
 	measure(c)
 
-	// `detectCircle` takes structs that satisfy the `geometry` interface
-	// if the struct is of type `circle`, it prints out the radius.
-	detectCircle(r) // doesn't print anything.
+	detectCircle(r)
 	detectCircle(c)
-
 }

examples/interfaces/interfaces.hash

@@ -1,2 +1,2 @@
-9a362e2c9aed98013fa9b91af81d6cc373979db6
-tfsLP7R0dtH
+6324a4bdb756a0ec2ccc60e13c97d2650e730ed6
+xAAbgd7GOKD

examples/interfaces/interfaces.sh

@@ -5,7 +5,7 @@ $ go run interfaces.go
 {5}
 78.53981633974483
 31.41592653589793
-5
+circle with radius 5
 
-# To learn more about Go's interfaces, check out this
-# [great blog post](https://jordanorelli.tumblr.com/post/32665860244/how-to-use-interfaces-in-go).
+# To understand how Go's interfaces work under the hood,
+# check out this [blog post](https://research.swtch.com/interfaces).