Note that while interface upgrades are very usefull to use, they are not something very new in the programming language world. In java you could do: if (rea

Note that while interface upgrades are very usefull to use, they are not something very new in the programming language world. In java you could do: if (reader instanceOf BufferedReader) { // upgrade BufferedReader bReader = (BufferedReader) reader; } This is actualy adviced NOT to do, since its really a runtime type check. In Go its no different, as this article explains. However its still a usefull mechanism sometimes.