Embedding a struct declaration in a text template in Go

Here’s a nice little technique I came across in developing gen.

Say you have a text template, and that template is intended to output Go code. You’d like to pass a data structure into the template, and have the structure appear in the template as its own value literal.

There is a printf format string verb that does just this: %#v

Let’s say you have a template like: p := {{.}}, where {{.}} represents the passed-in data. Let’s say the data is a struct.

type Person struct {  
	Name string  
	Age int  
}

person := Person{"Jane", 30}  

In order to have the output work as we wish, we make this modification to the template:

p := {{ printf "%#v" . }}

…which means “call printf with the format string %#v and the value ., which represents the passed data”.

We execute the template along the lines of: tmpl.Execute(w, person) (Where tmpl is the compiled template, and w is an io.Writer)

The resulting output will be:

p := pkg.Person{Name:"Jane", Age:30}

…where pkg is your package name. Thats valid Go code which in turn can be executed. Neat.

Here’s a runnable version on the Go playground.