iteration

for/readme.md

@@ -0,0 +1,112 @@
+# for
+
+To do stuff repeatedly in Go, you'll need `for`. In go there are no `while`, `do`, `until` kewords, you can only use `for`. Which is a good thing!
+
+## Repeat a character
+
+Let's write a test for a function that repeats a character 5 times.
+
+There's nothing new so far, so try and write it yourself for practice.
+
+```go
+package main
+
+import "testing"
+
+func TestRepeat(t *testing.T) {
+	repeated := Repeat("a")
+	expected := "aaaaa"
+
+	if repeated != expected {
+		t.Errorf("expected '%s' but got '%s'", expected, repeated)
+	}
+}
+```
+
+_Keep the discipline!_ You will dont need to know anything new right now
+
+- Run the test
+- Listen to the compiler
+- Make it compile
+
+```go
+package main
+
+func Repeat(character string) (repeated string)  {
+	return
+}
+```
+
+Isn't it nice to know you already know enough Go to write tests for some basic problems? This means you can now play with the production code as much as you like and know it's behaving as you'd hope.
+
+The `for` syntax is very unremarkable and follows most C-like languages.
+
+```go
+func Repeat(character string) (repeated string) {
+	for i := 0; i < 5; i++ {
+		repeated = repeated + character
+	}
+	return
+}
+```
+
+Run the test and it should pass. 
+
+Now it's time to refactor and introduce another construct `+=`
+
+```go
+const repeatCount = 5
+
+func Repeat(character string) (repeated string) {
+	for i := 0; i < repeatCount; i++ {
+		repeated += character
+	}
+	return
+}
+```
+
+`+=` adds a value to another. It works other types like integers.
+
+## next iteration
+
+todo: Think of a way to include `continue` in exercise.
+
+## Benchmarking
+
+Writing benchmarks in Go is another first-class feature of the language and it is very similar to writing tests. 
+
+```go
+func BenchmarkRepeat(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		Repeat("a")
+	}
+}
+```
+
+I am using gogland so when I type `Test` or `Bench` in a file it generates most of the code for me. 
+
+You'll see the code is very similar to a test.
+
+The `testing.B` gives you access to the cryptically named `b.N`. 
+
+When the benchmark is run the code is ran `b.N` times, and measure how long it takes. 
+
+That amount shouldn't matter to you, the framework will determine what is a "good" value for that to let you have some decent results.
+
+To run the benchmarks do `go test -bench=.`
+
+```
+goos: darwin
+goarch: amd64
+pkg: github.com/quii/learn-go-with-tests/for/v4
+10000000	       136 ns/op
+PASS
+```
+
+What that means is our function takes 136 nanoseconds to run. Which is pretty ok!
+
+### Practice exercises
+
+- Change the test so a caller can specify how many times the character is repeated and then fix the code
+- Write `ExampleRepeat` to document your function
+- Have a look through the [the strings package](https://golang.org/pkg/strings)  package. Find functions you think could be useful and experiment with them by writing tests like we have here. Investing time learning the standard library will really pay off over time.

for/v1/repeat.go

@@ -0,0 +1,5 @@
+package main
+
+func Repeat(character string) (repeated string)  {
+	return
+}

for/v1/repeat_test.go

@@ -0,0 +1,12 @@
+package main
+
+import "testing"
+
+func TestRepeat(t *testing.T) {
+	repeated := Repeat("a")
+	expected := "aaaaa"
+
+	if repeated != expected {
+		t.Errorf("expected '%s' but got '%s'", expected, repeated)
+	}
+}

for/v2/repeat.go

@@ -0,0 +1,8 @@
+package main
+
+func Repeat(character string) (repeated string) {
+	for i := 0; i < 5; i++ {
+		repeated = repeated + character
+	}
+	return
+}

for/v2/repeat_test.go

@@ -0,0 +1,12 @@
+package main
+
+import "testing"
+
+func TestRepeat(t *testing.T) {
+	repeated := Repeat("a")
+	expected := "aaaaa"
+
+	if repeated != expected {
+		t.Errorf("expected '%s' but got '%s'", expected, repeated)
+	}
+}

for/v3/repeat.go

@@ -0,0 +1,10 @@
+package main
+
+const repeatCount = 5
+
+func Repeat(character string) (repeated string) {
+	for i := 0; i < repeatCount; i++ {
+		repeated += character
+	}
+	return
+}

for/v3/repeat_test.go

@@ -0,0 +1,12 @@
+package main
+
+import "testing"
+
+func TestRepeat(t *testing.T) {
+	repeated := Repeat("a")
+	expected := "aaaaa"
+
+	if repeated != expected {
+		t.Errorf("expected '%s' but got '%s'", expected, repeated)
+	}
+}

for/v4/repeat.go

@@ -0,0 +1,10 @@
+package main
+
+const repeatCount = 5
+
+func Repeat(character string) (repeated string) {
+	for i := 0; i < repeatCount; i++ {
+		repeated += character
+	}
+	return
+}

for/v4/repeat_test.go

@@ -0,0 +1,12 @@
+package main
+
+import "testing"
+
+func TestRepeat(t *testing.T) {
+	repeated := Repeat("a")
+	expected := "aAaAa"
+
+	if repeated != expected {
+		t.Errorf("expected '%s' but got '%s'", expected, repeated)
+	}
+}

for/vx/repeat.go

@@ -0,0 +1,10 @@
+package main
+
+const repeatCount = 5
+
+func Repeat(character string) (repeated string) {
+	for i := 0; i < repeatCount; i++ {
+		repeated += character
+	}
+	return
+}

for/vx/repeat_test.go

@@ -0,0 +1,18 @@
+package main
+
+import "testing"
+
+func TestRepeat(t *testing.T) {
+	repeated := Repeat("a")
+	expected := "aaaaa"
+
+	if repeated != expected {
+		t.Errorf("expected '%s' but got '%s'", expected, repeated)
+	}
+}
+
+func BenchmarkRepeat(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		Repeat("a")
+	}
+}

integers/v1/adder_test.go

@@ -2,6 +2,7 @@ package main
 
 import "testing"
 
+
 func TestAdder(t *testing.T) {
 	sum := Add(2, 2)
 	expected := 4

readme.md

@@ -1,10 +1,12 @@
 # Learn go with tests
 
+I hope that after reading this you'll have a good grasp of the Go language in terms of its syntax, tooling and idioms - and be confident you will be able to start writing great systems in Go. 
+
 I have some experience introducing Go to development teams and have tried different approaches as to how to grow a team from some people curious about Go into highly effective writers of Go systems.
 
 ## What didnt work
 
-### Read a book
+### Read _the_ book
 
 An approach we tried was to take [the blue book](https://www.amazon.co.uk/Programming-Language-Addison-Wesley-Professional-Computing/dp/0134190440) and every week discuss the next chapter along with the exercises. 
 
@@ -53,6 +55,7 @@ Taking my experience of learning with a group and my own personal way I am going
 
 1. [Hello, world](/hello-world) - Declaring variables, constants, if statements, write your first go program and write your first test.
 2. [Integers](/integers) - Further Explore function declaration syntax and learn new ways to improve the documentation of your code.
+3. [Iteration](/for) - Learn about `for` and benchmarking
 
 Property based tests (todo)