{"id":5510,"date":"2018-09-11T20:25:35","date_gmt":"2018-09-11T20:25:35","guid":{"rendered":"https:\/\/www.modernescpp.com\/index.php\/c-core-guidelines-type-erasure-with-templates\/"},"modified":"2023-06-26T11:45:05","modified_gmt":"2023-06-26T11:45:05","slug":"c-core-guidelines-type-erasure-with-templates","status":"publish","type":"post","link":"https:\/\/www.modernescpp.com\/index.php\/c-core-guidelines-type-erasure-with-templates\/","title":{"rendered":"C++ Core Guidelines: Type Erasure with Templates"},"content":{"rendered":"

In the last post C++ Core Guidelines: Type Erasure<\/a>, I presented two ways to implement type erasure: void pointers and object orientation. In this post, I bridge dynamic polymorphism (object orientation) with static polymorphism (templates) to get type erasure with templates.<\/p>\n

<\/p>\n

 \"\"<\/p>\n

As our starting point and reminder, here is type erasure based on object orientation.<\/p>\n

Type erasure with object-orientation<\/h2>\n

Type erasure with object-orientation boils down to an inheritance hierarchy.<\/p>\n

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\/\/ typeErasureOO.cpp<\/span>\r\n\r\n#include <iostream><\/span>\r\n#include <string><\/span>\r\n#include <vector><\/span>\r\n\r\nstruct<\/span> BaseClass{                                     \/\/ (2)<\/span>\r\n\tvirtual<\/span> std::<\/span>string getName() const<\/span> =<\/span> 0<\/span>;\r\n};\r\n\r\nstruct<\/span> Bar:<\/span> BaseClass{\r\n\tstd::<\/span>string getName() const<\/span> override {\r\n\t    return<\/span> \"Bar\"<\/span>;\r\n\t}\r\n};\r\n\r\nstruct<\/span> Foo:<\/span> BaseClass{\r\n\tstd::<\/span>string getName() const<\/span> override{\r\n\t    return<\/span> \"Foo\"<\/span>;\r\n\t}\r\n};\r\n\r\nvoid<\/span> printName<\/span>(std::<\/span>vector<<\/span>const<\/span> BaseClass*><\/span> vec){    \/\/ (3)<\/span>\r\n    for<\/span> (auto<\/span> v:<\/span> vec) std::<\/span>cout <<<\/span> v-><\/span>getName() <<<\/span> std::<\/span>endl;\r\n}\r\n\r\n\r\nint<\/span> main<\/span>(){\r\n\t\r\n\tstd::<\/span>cout <<<\/span> std::<\/span>endl;\r\n\t\r\n\tFoo foo;\r\n\tBar bar; \r\n\t\r\n\tstd::<\/span>vector<<\/span>const<\/span> BaseClass*><\/span> vec{&<\/span>foo, &<\/span>bar};    \/\/ (1)<\/span>\r\n\t\r\n\tprintName(vec);\r\n\t\r\n\tstd::<\/span>cout <<<\/span> std::<\/span>endl;\r\n\r\n}\r\n<\/pre>\n<\/div>\n
 <\/p>\n
The key point is that you can use instances of Foo<\/code> or Bar<\/code> instead of an instance for BaseClass.<\/code> For further details, read the post C++ Core Guidelines: Type Erasure.<\/a><\/p>\n
What are the pros and cons of this implementation with OO?<\/p>\n
Pros:<\/strong><\/p>\n