使用范围从模板构建时，Go无法评估字段

I have Files slice of File structure in my Go program to keep name and size of files. I created template, see below:

type File struct {
    FileName string
    FileSize int64
}
var Files []File
const tmpl = `
    {{range .Files}}
    file {{.}}
    {{end}}
    `
t := template.Must(template.New("html").Parse(tmplhtml))
    err = t.Execute(os.Stdout, Files)
    if err != nil { panic(err) }

Of course I got panic saying:

can't evaluate field Files in type []main.File

Not sure how to correctly display file names and sizes using range in template.

The initial value of your pipeline (the dot) is the value you pass to Template.Execute() which in your case is Files which is of type []File.

So during your template execution the dot . is []File. This slice has no field or method named Files which is what .Files would refer to in your template.

What you should do is simply use . which refers to your slice:

const tmpl = `
    {{range .}}
    file {{.}}
    {{end}}
`

And that's all. Testing it:

var Files []File = []File{
    File{"data.txt", 123},
    File{"prog.txt", 5678},
}
t := template.Must(template.New("html").Parse(tmpl))
err := t.Execute(os.Stdout, Files)

Output (try it on the Go Playground):

file {data.txt 123}

file {prog.txt 5678}