controller.rb

class PostsController < ApplicationController
  def index
  end

  def new
    @post = Post.new(date: params[:date])
  end

  private

  def post_params
    params.require(:post).permit(:title, :date)
  end
end

new.html.erb

<p style="color: green"><%= notice %></p>

<h1>Posts</h1>

<%= link_to "New post", new_post_path %>
<%= link_to "New post TODAY", new_post_path(date: Date.today) %>