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    <p>It's true that you can use <code>||=</code> in this way, but it's a very strange thing to set the params <em>after</em> retrieving them. It's more likely you'll be setting variables <em>from</em> the params. So instead of this:</p> <pre><code>params[:start] ||= 0 </code></pre> <p>surely you're more likely to be doing this:</p> <pre><code>start = params[:start] || 0 </code></pre> <p>and if you're going to do that then I'd suggest using <a href="http://www.ruby-doc.org/core-1.9.3/Hash.html#method-i-fetch" rel="nofollow">fetch</a></p> <pre><code>start = params.fetch :start, 0 </code></pre> <p>If you're <em>really</em> looking for default values in the parameters hash before a route, then use a <a href="http://www.sinatrarb.com/intro.html#Filters" rel="nofollow">before filter</a></p> <pre><code>before "/comments/?" do params[:start] ||= 0 end </code></pre> <hr> <h3>Update:</h3> <p>If you're taking a parameter <strong>from the route pattern</strong> then you can give it a default argument by using block parameters, because Ruby (from v1.9) can take default parameters for blocks, e.g.</p> <pre><code>get "/comments/:start/?" do |start=0| # rest of code here end </code></pre> <p>The <code>start</code> parameter will be available via the <code>start</code> local variable (given to the block) or via <code>params[:captures].first</code> (see <a href="http://www.sinatrarb.com/intro#Routes" rel="nofollow">the docs for more on routes</a>).</p> <hr> <h3>Further update:</h3> <p>When you pass a route to a verb method (e.g. <code>get</code>) the Sinatra will use that route to match incoming requests against. Requests that match fire the block given, so a simple way to make clear that you want some defaults would be:</p> <pre><code>get "/comments/?" do defaults = {start: 10, finish: 20} params = defaults.merge params # more code follows… end </code></pre> <p>If you want it to look cleaner, use a helper:</p> <pre><code>helpers do def set_defaults( defaults={} ) warn "Entering set_defaults" # stringify_keys! h = defaults.each_with_object({}) do |(k,v),h| h[k.to_s] = defaults[k] end params.merge!( h.merge params ) end end get "/comments/?" do set_defaults start: 10, finish: 20 # more code follows… end </code></pre> <p>If you need something more heavyweight, try <a href="https://github.com/mattt/sinatra-param" rel="nofollow">sinatra-param</a>.</p> <hr> <h3>Sinatra::DefaultParameters gem</h3> <p>I liked this bit of code so much <a href="https://rubygems.org/gems/sinatra-default_parameters" rel="nofollow">I've turned it into a gem</a>.</p>
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    1. CO'but it's a very strange thing to set the params after retrieving them', agreed, that is why I called it a little 'hacky'. I am not sure a before filter is much better. I was really hoping for something like get '/comments[:start = 0]/?' or something similar. Seems pretty common to be able to do that with Routing frameworks.
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    2. CO@forumuser I've updated the answer for you.
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    3. COThanks iain, looks like the thought about 'path' parameter defaults but not url parameter defaults, i.e. /comments?status. Looks like there is no perfect answer at this point.
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