Add methods for prefixing and suffixing

Closes #5

Add methods for prefixing and suffixing

Closes #5

README.md

@@ -332,6 +332,26 @@ LcFirst simply returns result by lower casing first letter of string and it can
 ```
 
 
+#### Prefix(string) string
+
+Prefix makes sure string has been prefixed with a given string and avoids adding it again if it has.
+
+```go
+ufo := stringy.New("known flying object")
+fmt.Println(ufo.Prefix("un")) // unknown flying object
+```
+
+
+#### Suffix(string) string
+
+Suffix makes sure string has been suffixed with a given string and avoids adding it again if it has.
+
+```go
+pun := stringy.New("this really is a cliff")
+fmt.Println(pun.Suffix("hanger")) // this really is a cliffhanger
+```
+
+
 ## Running the tests
 
 ``` bash

example/main.go

@@ -74,4 +74,9 @@ func main() {
 	last := lcn.Last(4)
 	fmt.Println(last) // 1348
 
+	ufo := stringy.New("known flying object")
+	fmt.Println(ufo.Prefix("un")) // unknown flying object
+
+	pun := stringy.New("this really is a cliff")
+	fmt.Println(pun.Suffix("hanger")) // this really is a cliffhanger
 }

stringy.go

@@ -41,6 +41,8 @@ type StringManipulation interface {
 	ToLower() string
 	ToUpper() string
 	UcFirst() string
+	Prefix(with string) string
+	Suffix(with string) string
 }
 
 // New func returns pointer to input struct
@@ -329,3 +331,23 @@ func (i *input) UcFirst() string {
 	input := getInput(*i)
 	return ucfirst(input)
 }
+
+// Prefix makes sure that string is prefixed with a given string
+func (i *input) Prefix(with string) string {
+	input := getInput(*i)
+	if strings.HasPrefix(input, with) {
+		return input
+	}
+
+	return with + input
+}
+
+// Suffix makes sure that string is suffixed with a given string
+func (i *input) Suffix(with string) string {
+	input := getInput(*i)
+	if strings.HasSuffix(input, with) {
+		return input
+	}
+
+	return input + with
+}

stringy_test.go

@@ -1,6 +1,7 @@
 package stringy
 
 import (
+	"fmt"
 	"testing"
 )
 
@@ -310,3 +311,29 @@ func TestInput_Last(t *testing.T) {
 		t.Errorf("Expected: to be %s but got: %s", against, last)
 	}
 }
+
+func ExampleStringManipulation_Prefix() {
+	fmt.Println(New("foobar").Prefix("foo"))
+	fmt.Println(New("foobar").Prefix("foofoo"))
+	fmt.Println(New("foobar").Prefix("/"))
+	fmt.Println(New("").Prefix("_"))
+	// Output:
+	// foobar
+	// foofoofoobar
+	// /foobar
+	// _
+}
+
+func ExampleStringManipulation_Suffix() {
+	fmt.Println(New("foobar").Suffix("bar"))
+	fmt.Println(New("foobar").Suffix("barbar"))
+	fmt.Println(New("foobar").Suffix("/"))
+	fmt.Println(New("foobar/").Suffix("/"))
+	fmt.Println(New("").Suffix("_"))
+	// Output:
+	// foobar
+	// foobarbarbar
+	// foobar/
+	// foobar/
+	// _
+}