Factory Method: a creation point inside a shared workflow

3a:I[286652,["$20","$21","$22","$23","$24","$2e"],"default"] 3b:T247e,{"type":"doc","content":[{"type":"heading","attrs":{"level":2},"content":[{"type":"text","text":"Overview"}]},{"type":"paragraph","content":[{"type":"text","text":"Export jobs share a workflow, but CSV and JSON jobs need different writers. Repeating the whole workflow merely to change its writer makes maintenance harder."}]},{"type":"paragraph","content":[{"type":"text","text":"Factory Method lets a subclass override the method that creates a product. The base workflow uses the product through its common interface."}]},{"type":"heading","attrs":{"level":2},"content":[{"type":"text","text":"UML"}]},{"type":"animatedDiagramBlock","attrs":{"title":"Factory Method: a creation point inside a shared workflow","scene":{"svg":"","css":"","javascript":""},"width":0,"height":590,"autoplay":false,"showControls":false,"fitMode":"contain","frameMode":"content"}},{"type":"paragraph","content":[{"type":"text","text":"ExportJob.Run() obtains an IWriter through Create(). CsvJob and JsonJob override Create() while sharing the base Run() implementation."}]},{"type":"heading","attrs":{"level":2},"content":[{"type":"text","text":"History"}]},{"type":"paragraph","content":[{"type":"text","text":"GoF cataloged Factory Method as a creational pattern in Design Patterns in 1994. It delegates a concrete creation choice to subclasses."},{"type":"footnote","attrs":{"id":"factory-method-gof","body":"Gamma, Helm, Johnson, Vlissides. *Design Patterns* (1994). [Publisher record](https://www.informit.com/store/design-patterns-elements-of-reusable-object-oriented-software-9780201633610). Creational patterns, Factory Method."}}]},{"type":"heading","attrs":{"level":2},"content":[{"type":"text","text":"Why use it?"}]},{"type":"paragraph","content":[{"type":"text","text":"A new writer can reuse the workflow. The creation method identifies where the concrete product is chosen."}]},{"type":"paragraph","content":[{"type":"text","text":"A static function that returns an object is often called a factory function. The specific mechanism here is overriding a creation method through inheritance; an already-injected writer may make this hierarchy unnecessary."}]},{"type":"heading","attrs":{"level":2},"content":[{"type":"text","text":"Example"}]},{"type":"paragraph","content":[{"type":"text","text":"CsvJob creates the CSV writer, and the shared ExportJob.Run() uses it."}]},{"type":"codeBlock","attrs":{"language":"csharp"},"content":[{"type":"text","text":"using System;\nusing System.Collections.Generic;\nusing System.Linq;\n\nConsole.WriteLine(new CsvJob().Run());\n\ninterface IWriter { string Write(string value); }\nsealed class CsvWriter : IWriter\n{\n public string Write(string value) => \"\\\"\" + value.Replace(\"\\\"\", \"\\\"\\\"\") + \"\\\"\";\n}\nsealed class JsonWriter : IWriter\n{\n public string Write(string value) => System.Text.Json.JsonSerializer.Serialize(new { value });\n}\nabstract class ExportJob\n{\n protected abstract IWriter Create();\n public string Run() => Create().Write(\"hello\");\n}\nsealed class CsvJob : ExportJob\n{\n protected override IWriter Create() => new CsvWriter();\n}\nsealed class JsonJob : ExportJob\n{\n protected override IWriter Create() => new JsonWriter();\n}\n"}]},{"type":"codeBlock","attrs":{"language":"text"},"content":[{"type":"text","text":"\"hello\""}]},{"type":"paragraph","content":[{"type":"text","text":"Run() never constructs CsvWriter directly. Choosing a job implementation is separate from the shared workflow."}]},{"type":"heading","attrs":{"level":2},"content":[{"type":"text","text":"An extended example"}]},{"type":"paragraph","content":[{"type":"text","text":"Add a JSON job and run both through ExportJob. The JSON serializer handles string escaping rather than assembling JSON by concatenation."}]},{"type":"codeBlock","attrs":{"language":"csharp"},"content":[{"type":"text","text":"using System;\nusing System.Collections.Generic;\nusing System.Linq;\n\nforeach (ExportJob job in new ExportJob[] { new CsvJob(), new JsonJob() })\n Console.WriteLine(job.Run());\n\ninterface IWriter { string Write(string value); }\nsealed class CsvWriter : IWriter\n{\n public string Write(string value) => \"\\\"\" + value.Replace(\"\\\"\", \"\\\"\\\"\") + \"\\\"\";\n}\nsealed class JsonWriter : IWriter\n{\n public string Write(string value) => System.Text.Json.JsonSerializer.Serialize(new { value });\n}\nabstract class ExportJob\n{\n protected abstract IWriter Create();\n public string Run() => Create().Write(\"hello\");\n}\nsealed class CsvJob : ExportJob\n{\n protected override IWriter Create() => new CsvWriter();\n}\nsealed class JsonJob : ExportJob\n{\n protected override IWriter Create() => new JsonWriter();\n}\n"}]},{"type":"codeBlock","attrs":{"language":"text"},"content":[{"type":"text","text":"\"hello\"\n{\"value\":\"hello\"}"}]},{"type":"paragraph","content":[{"type":"text","text":"Run() stays the same while Create() returns different products. A Factory Method can also be one of the customizable steps inside a Template Method."}]},{"type":"heading","attrs":{"level":2},"content":[{"type":"text","text":"Related reading"}]},{"type":"bulletList","content":[{"type":"listItem","content":[{"type":"paragraph","content":[{"type":"text","text":"Programming patterns","marks":[{"type":"link","attrs":{"href":"https://www.makonea.com/en-US/wiki/programming-patterns","target":null,"rel":null}}]}]}]},{"type":"listItem","content":[{"type":"paragraph","content":[{"type":"text","text":"Abstract Factory Pattern","marks":[{"type":"link","attrs":{"href":"https://www.makonea.com/en-US/wiki/abstract-factory-pattern","target":null,"rel":null}}]}]}]},{"type":"listItem","content":[{"type":"paragraph","content":[{"type":"text","text":"Template Method Pattern","marks":[{"type":"link","attrs":{"href":"https://www.makonea.com/en-US/wiki/template-method-pattern","target":null,"rel":null}}]}]}]}]},{"type":"paragraph","content":[{"type":"text","text":"Each example is a separate .NET 10 console program."}]}]}3c:T2492,{"type":"doc","content":[{"type":"heading","attrs":{"level":2},"content":[{"type":"text","text":"Overview"}]},{"type":"paragraph","content":[{"type":"text","text":"Export jobs share a workflow, but CSV and JSON jobs need different writers. Repeating the whole workflow merely to change its writer makes maintenance harder."}]},{"type":"paragraph","content":[{"type":"text","text":"Factory Method lets a subclass override the method that creates a product. The base workflow uses the product through its common interface."}]},{"type":"heading","attrs":{"level":2},"content":[{"type":"text","text":"UML"}]},{"type":"animatedDiagramBlock","attrs":{"title":"Factory Method: a creation point inside a shared workflow","scene":{"svg":"","css":"","javascript":""},"width":0,"height":590,"autoplay":false,"showControls":false,"fitMode":"contain","frameMode":"content"}},{"type":"paragraph","content":[{"type":"text","text":"ExportJob.Run() obtains an IWriter through Create(). CsvJob and JsonJob override Create() while sharing the base Run() implementation."}]},{"type":"heading","attrs":{"level":2},"content":[{"type":"text","text":"History"}]},{"type":"paragraph","content":[{"type":"text","text":"GoF cataloged Factory Method as a creational pattern in Design Patterns in 1994. It delegates a concrete creation choice to subclasses."},{"type":"footnote","attrs":{"id":"factory-method-gof","body":"Gamma, Helm, Johnson, Vlissides. *Design Patterns* (1994). [Publisher record](https://www.informit.com/store/design-patterns-elements-of-reusable-object-oriented-software-9780201633610). Creational patterns, Factory Method."}}]},{"type":"heading","attrs":{"level":2},"content":[{"type":"text","text":"Why use it?"}]},{"type":"paragraph","content":[{"type":"text","text":"A new writer can reuse the workflow. The creation method identifies where the concrete product is chosen."}]},{"type":"paragraph","content":[{"type":"text","text":"A static function that returns an object is often called a factory function. The specific mechanism here is overriding a creation method through inheritance; an already-injected writer may make this hierarchy unnecessary."}]},{"type":"heading","attrs":{"level":2},"content":[{"type":"text","text":"Example"}]},{"type":"paragraph","content":[{"type":"text","text":"CsvJob creates the CSV writer, and the shared ExportJob.Run() uses it."}]},{"type":"codeBlock","attrs":{"language":"csharp"},"content":[{"type":"text","text":"using System;\nusing System.Collections.Generic;\nusing System.Linq;\n\nConsole.WriteLine(new CsvJob().Run());\n\ninterface IWriter { string Write(string value); }\nsealed class CsvWriter : IWriter\n{\n public string Write(string value) => \"\\\"\" + value.Replace(\"\\\"\", \"\\\"\\\"\") + \"\\\"\";\n}\nsealed class JsonWriter : IWriter\n{\n public string Write(string value) => System.Text.Json.JsonSerializer.Serialize(new { value });\n}\nabstract class ExportJob\n{\n protected abstract IWriter Create();\n public string Run() => Create().Write(\"hello\");\n}\nsealed class CsvJob : ExportJob\n{\n protected override IWriter Create() => new CsvWriter();\n}\nsealed class JsonJob : ExportJob\n{\n protected override IWriter Create() => new JsonWriter();\n}\n"}]},{"type":"codeBlock","attrs":{"language":"text"},"content":[{"type":"text","text":"\"hello\""}]},{"type":"paragraph","content":[{"type":"text","text":"Run() never constructs CsvWriter directly. Choosing a job implementation is separate from the shared workflow."}]},{"type":"heading","attrs":{"level":2},"content":[{"type":"text","text":"An extended example"}]},{"type":"paragraph","content":[{"type":"text","text":"Add a JSON job and run both through ExportJob. The JSON serializer handles string escaping rather than assembling JSON by concatenation."}]},{"type":"codeBlock","attrs":{"language":"csharp"},"content":[{"type":"text","text":"using System;\nusing System.Collections.Generic;\nusing System.Linq;\n\nforeach (ExportJob job in new ExportJob[] { new CsvJob(), new JsonJob() })\n Console.WriteLine(job.Run());\n\ninterface IWriter { string Write(string value); }\nsealed class CsvWriter : IWriter\n{\n public string Write(string value) => \"\\\"\" + value.Replace(\"\\\"\", \"\\\"\\\"\") + \"\\\"\";\n}\nsealed class JsonWriter : IWriter\n{\n public string Write(string value) => System.Text.Json.JsonSerializer.Serialize(new { value });\n}\nabstract class ExportJob\n{\n protected abstract IWriter Create();\n public string Run() => Create().Write(\"hello\");\n}\nsealed class CsvJob : ExportJob\n{\n protected override IWriter Create() => new CsvWriter();\n}\nsealed class JsonJob : ExportJob\n{\n protected override IWriter Create() => new JsonWriter();\n}\n"}]},{"type":"codeBlock","attrs":{"language":"text"},"content":[{"type":"text","text":"\"hello\"\n{\"value\":\"hello\"}"}]},{"type":"paragraph","content":[{"type":"text","text":"Run() stays the same while Create() returns different products. A Factory Method can also be one of the customizable steps inside a Template Method."}]},{"type":"heading","attrs":{"level":2},"content":[{"type":"text","text":"Related reading"}]},{"type":"bulletList","content":[{"type":"listItem","content":[{"type":"paragraph","content":[{"type":"text","text":"Programming patterns","marks":[{"type":"link","attrs":{"href":"https://www.makonea.com/en-US/wiki/programming-patterns","target":null,"rel":null}}]}]}]},{"type":"listItem","content":[{"type":"paragraph","content":[{"type":"text","text":"Abstract Factory Pattern","marks":[{"type":"link","attrs":{"href":"https://www.makonea.com/en-US/wiki/abstract-factory-pattern","target":null,"rel":null}}]}]}]},{"type":"listItem","content":[{"type":"paragraph","content":[{"type":"text","text":"Template Method Pattern","marks":[{"type":"link","attrs":{"href":"https://www.makonea.com/en-US/wiki/template-method-pattern","target":null,"rel":null}}]}]}]}]},{"type":"paragraph","content":[{"type":"text","text":"Each example is a separate .NET 10 console program."}]}]}1c:["$","div",null,{"className":"mx-auto max-w-6xl space-y-5 px-4 py-8 sm:py-12","children":[["$","$L2f",null,{"href":"/en-US/wiki/factory-method-pattern/history","className":"underline","children":["← ","Revision history"]}],["$","h1",null,{"className":"text-2xl font-bold","children":"Compare revisions"}],[["$","h2",null,{"className":"break-words text-xl font-bold","children":"Factory Method Pattern"}],["$","p",null,{"className":"text-sm","children":"Body changes between the two selected stored revisions. 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