json.go

"$matchOne": func(template, context map[string]interface{}) (interface{}, error) {
		if err := restrictProperties(template, "$matchOne"); err != nil {
			return nil, err
		}

		match, ok := template["$matchOne"].(map[string]interface{})
		if !ok {
			return nil, TemplateError{
				Message:  "$matchOne can evaluate objects only",
				Template: template,
			}
		}

		// get the sorted list of conditions
		conditions := make([]string, 0, len(match))
		for condition := range match {
			conditions = append(conditions, condition)
		}
		sort.Strings(conditions)

		result := ""

		for _, key := range conditions {
			check, err := i.Execute(key, 0, context)
			if err != nil {
				return nil, TemplateError{
					Message:  err.Error(),
					Template: template,
				}
			}

			if i.IsTruthy(check) {
				value := match[key]
				r, err := render(value, context)
				if err != nil {
					return nil, TemplateError{
						Message:  err.Error(),
						Template: template,
					}
				}
				result = fmt.Sprintf("%v", r)
				break
			}
		}

		return result, nil
	},