refactor: common ifaces

interfaces/_old/09-stringer/_handlemethods.go

@@ -0,0 +1,46 @@
+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+// In the depths of the Go standard library's fmt package...
+// Printing functions use the handleMethods method.
+
+// Example:
+// var pocket money = 10
+// fmt.Println(pocket)
+
+//            the argument can be any type of value
+//      stores the pocket variable in the argument variable
+//                            ^
+//                            |
+func (p *pp) handleMethods(argument interface{}) (handled bool) {
+	// ...
+
+	// Checks whether a given argument is an error or an fmt.Stringer
+	switch v := argument.(type) {
+	// ...
+	// If the argument is a Stringer, calls its String() method
+	case Stringer:
+		// ...
+		//        pocket.String()
+		//              ^
+		//              |
+		p.fmtString(v.String(), verb)
+		return
+	}
+
+	// ...
+}
+
+/*
+The original `handleMethods` code is more involved:
+
+https://github.com/golang/go/blob/6f51082da77a1d4cafd5b7af0db69293943f4066/src/fmt/print.go#L574
+
+	-> 574#handleMethods(..)
+	-> 627#Stringer type check: If `v` is a Stringer, run:
+	-> 630#v.String()
+*/