Allow injecting into helper functions

[codegangsta]

from @ahall

The goal is to be able to do something like this:

m.Use(render.Renderer(render.Options{
    Layout:    "layout",
    Funcs: []template.FuncMap{
        {
            "myCustomFunc": func(r *http.Request, m MyInjectedStuff) string {
                                    // Do something with r and m
                return "My custom function"
            },
        },
    },
}))

Original issue:
https://github.com/codegangsta/martini-contrib/issues/99

[ahall]

Hi @codegangsta. Have you had time to think about this?

[sevkin]

very useful. it will be possible to inject render.Render?

[seedifferently]

Definitely needed. I'd also like to be able to inject values from sessions.Session.

[ahall]

Yep, now just waiting feedback from the mighty @codegangsta

[codegangsta]

Yeah this would be great to have. There are some unfortunate limitation as to how Go's template library works with helper functions. There may be some clever ways to do so. But most of the solutions seem overly hacky.

[scottkf]

The only thing that appears to work is defining a stub method, then including a middleware overriding the template maps (which injects anything I need, like session, etc). The only thing that might make it easier is not having to define the method in the beginning, but golang's text/template doesn't appear to work that way. Might be some hackish way to implement it though.

m.Use(render.Renderer(render.Options{
  Extensions: []string{".tmpl", ".html"},
  Funcs:      funcHeader}))
m.Use(HelperFuncs())

var funcHeader = []template.FuncMap{
    {
        "set_data": func(context map[string]interface{}) string {
            return ""
        },
    }
}

func HelperFuncs() martini.Handler {
    return func(r render.Render, u *users.UserProfile, s sessions.Session) {
        r.Template().Funcs(funcDefinitions(u, s))
    }
}

var funcDefinitions = func(u *users.UserProfile, s sessions.Session) template.FuncMap {
    return template.FuncMap{
        "set_data": func(context map[string]interface{}) string {
            do something with session
        }
    }
}