Use lazy String
evaluation "#{variable}"
:
def gravatar_for(user, show = nil)
gravatar_id = Digest::MD5::hexdigest(user.email.downcase)
gravatar_url = "https://secure.gravatar.com/avatar/#{gravatar_id}"
mod = "-show" if show
image_tag(gravatar_url, alt: user.name, class: "gravatar#{mod} img-rounded")
end