gobuffalo/velvet

package velvet

import (
    "bytes"
    "html/template"
    "reflect"

    "github.com/pkg/errors"
)

func eachHelper(collection interface{}, help HelperContext) (template.HTML, error) {
    out := bytes.Buffer{}
    val := reflect.ValueOf(collection)
    if val.Kind() == reflect.Ptr {
        val = val.Elem()
    }
    if val.Kind() == reflect.Struct || val.Len() == 0 {
        s, err := help.ElseBlock()
        return template.HTML(s), err
    }
    switch val.Kind() {
    case reflect.Array, reflect.Slice:
        for i := 0; i < val.Len(); i++ {
            v := val.Index(i).Interface()
            ctx := help.Context.New()
            ctx.Set("@first", i == 0)
            ctx.Set("@last", i == val.Len()-1)
            ctx.Set("@index", i)
            ctx.Set("@value", v)
            s, err := help.BlockWith(ctx)
            if err != nil {
                return "", errors.WithStack(err)
            }
            out.WriteString(s)
        }
    case reflect.Map:
        keys := val.MapKeys()
        for i := 0; i < len(keys); i++ {
            key := keys[i].Interface()
            v := val.MapIndex(keys[i]).Interface()
            ctx := help.Context.New()
            ctx.Set("@first", i == 0)
            ctx.Set("@last", i == len(keys)-1)
            ctx.Set("@key", key)
            ctx.Set("@value", v)
            s, err := help.BlockWith(ctx)
            if err != nil {
                return "", errors.WithStack(err)
            }
            out.WriteString(s)
        }
    }
    return template.HTML(out.String()), nil
}