From 8cbceb99c5951a65496cae12d111e77a2b3ff55e Mon Sep 17 00:00:00 2001 From: Serge Bishyr Date: Wed, 18 Oct 2017 16:31:29 +0300 Subject: [PATCH 1/3] behavioral/visitor: implement visitor pattern --- behavioral/visitor.md | 80 ++++++++++++++++++++++++++++++++++++++ behavioral/visitor/main.go | 64 ++++++++++++++++++++++++++++++ 2 files changed, 144 insertions(+) create mode 100644 behavioral/visitor.md create mode 100644 behavioral/visitor/main.go diff --git a/behavioral/visitor.md b/behavioral/visitor.md new file mode 100644 index 0000000..48a1088 --- /dev/null +++ b/behavioral/visitor.md @@ -0,0 +1,80 @@ +# Visitor Pattern +Visitor behavioral design pattern provides a way to separate an algorithm from an object on which it operates. + +It gives the ability to extend the existing object without modifying the object itself. + +## Implementation + +```go +type Visitor interface { + visitCircle(circle Circle) string + visitLine(line Line) string +} + +type Shape interface { + accept(Visitor) string +} + +type Circle struct { + Rad int +} + +func (c Circle) accept(v Visitor) string { + return v.visitCircle(c) +} + +type Line struct { + Len int +} + +func (l Line) accept(v Visitor) string { + return v.visitLine(l) +} +``` + +## Usage +### JSON marshaller + +```go +type JsonVisitor struct { +} + +func (*JsonVisitor) visitCircle(circle Circle) string { + return fmt.Sprintf(`{"type": "circle", "radius": "%v"}`, circle.Rad) +} + +func (*JsonVisitor) visitLine(line Line) string { + return fmt.Sprintf(`{"type": "line", "length": "%v"}`, line.Len) +} +``` + +```go +circle := Circle{12} +line := Line{42} +jsonVisitor := JsonVisitor{} +fmt.Println(circle.accept(&jsonVisitor)) +fmt.Println(line.accept(&jsonVisitor)) +``` + +### XML marshaller + +```go +type XmlVisitor struct { +} + +func (*XmlVisitor) visitCircle(circle Circle) string { + return fmt.Sprintf(`%d`, circle.Rad) +} + +func (*XmlVisitor) visitLine(line Line) string { + return fmt.Sprintf(`%d`, line.Len) +} +``` + +```go +circle := Circle{12} +line := Line{42} +xmlVisitor := XmlVisitor{} +fmt.Println(circle.accept(&xmlVisitor)) +fmt.Println(line.accept(&xmlVisitor)) +``` diff --git a/behavioral/visitor/main.go b/behavioral/visitor/main.go new file mode 100644 index 0000000..db9aa93 --- /dev/null +++ b/behavioral/visitor/main.go @@ -0,0 +1,64 @@ +package main + +import ( + "fmt" +) + +type Visitor interface { + visitCircle(circle Circle) string + visitLine(line Line) string +} + +type Shape interface { + accept(Visitor) string +} + +type Circle struct { + Rad int +} + +func (c Circle) accept(v Visitor) string { + return v.visitCircle(c) +} + +type Line struct { + Len int +} + +func (l Line) accept(v Visitor) string { + return v.visitLine(l) +} + +type JsonVisitor struct { +} + +func (*JsonVisitor) visitCircle(circle Circle) string { + return fmt.Sprintf(`{"type": "circle", "radius": "%v"}`, circle.Rad) +} + +func (*JsonVisitor) visitLine(line Line) string { + return fmt.Sprintf(`{"type": "line", "length": "%v"}`, line.Len) +} + +type XmlVisitor struct { +} + +func (*XmlVisitor) visitCircle(circle Circle) string { + return fmt.Sprintf(`%d`, circle.Rad) +} + +func (*XmlVisitor) visitLine(line Line) string { + return fmt.Sprintf(`%d`, line.Len) +} + +func main() { + circle := Circle{12} + line := Line{42} + jsonVisitor := JsonVisitor{} + fmt.Println(circle.accept(&jsonVisitor)) + fmt.Println(line.accept(&jsonVisitor)) + + xmlVisitor := XmlVisitor{} + fmt.Println(circle.accept(&xmlVisitor)) + fmt.Println(line.accept(&xmlVisitor)) +} From 7ba8e00dffe78410e00f8d2d04eac56fa3f02a7f Mon Sep 17 00:00:00 2001 From: Serge Bishyr Date: Wed, 18 Oct 2017 16:34:33 +0300 Subject: [PATCH 2/3] behavioral/visitor: marked visitor as implement in README --- README.md | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/README.md b/README.md index 7d9f5f7..783b90f 100644 --- a/README.md +++ b/README.md @@ -45,7 +45,7 @@ A curated collection of idiomatic design & application patterns for Go language. | [State](/behavioral/state.md) | Encapsulates varying behavior for the same object based on its internal state | ✘ | | [Strategy](/behavioral/strategy.md) | Enables an algorithm's behavior to be selected at runtime | ✔ | | [Template](/behavioral/template.md) | Defines a skeleton class which defers some methods to subclasses | ✘ | -| [Visitor](/behavioral/visitor.md) | Separates an algorithm from an object on which it operates | ✘ | +| [Visitor](/behavioral/visitor.md) | Separates an algorithm from an object on which it operates | ✔ | ## Synchronization Patterns From 6df1cb57f15c3aeed8e823b89f2a51adc7131b78 Mon Sep 17 00:00:00 2001 From: Serge Bishyr Date: Wed, 18 Oct 2017 16:38:00 +0300 Subject: [PATCH 3/3] behavioral/visitor: add more explanations to visitor implementation --- behavioral/visitor.md | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/behavioral/visitor.md b/behavioral/visitor.md index 48a1088..b6f3d11 100644 --- a/behavioral/visitor.md +++ b/behavioral/visitor.md @@ -4,6 +4,7 @@ Visitor behavioral design pattern provides a way to separate an algorithm from a It gives the ability to extend the existing object without modifying the object itself. ## Implementation +Implementation of a visitor that can add functionality to the shape structures. ```go type Visitor interface { @@ -34,7 +35,7 @@ func (l Line) accept(v Visitor) string { ## Usage ### JSON marshaller - +Using visitor to marshal shapes to JSON ```go type JsonVisitor struct { } @@ -57,7 +58,7 @@ fmt.Println(line.accept(&jsonVisitor)) ``` ### XML marshaller - +Using visitor to marshal shapes to XML ```go type XmlVisitor struct { }