The Go Programming Language

12.7 Accessing Struct Field Tags

In Section 4.5 we used struct field tags to modify the JSON encoding of Go struct values. The json field tag lets us choose alternative field names and suppress the output of empty fields. In this section, we’ll see how to access field tags using reflection.

In a web server, the first thing most HTTP handler functions do is extract the request parameters into local variables. We’ll define a utility function, params.Unpack, that uses struct field tags to make writing HTTP handlers (§7.7) more convenient.

First, we’ll show how it’s used. The search function below is an HTTP handler. It defines a variable called data of an anonymous struct type whose fields correspond to the HTTP request parameters. The struct’s ...