<p></p>
<p><b>@tomhughes</b> commented on this pull request.</p>

<p>I think I did look at this one before but I was concerned that where some of the things being joined were non-trivial expressions it might all become a bit unreadable.</p>
<p>As is often the case the style guide is unfortunately lacking in any rationale as to why you should prefer interpolation - my natural assumption would be that concatenation would generally be higher performance for example not that it matters most of the time.</p>
<p>I notice that <code>format</code> is an acceptable approach though, which would be easier to read where some of the things being interpolated are more complicated expressions.</p><hr>

<p>In <a href="https://github.com/openstreetmap/openstreetmap-website/pull/2921#discussion_r513619504">app/helpers/title_helper.rb</a>:</p>
<pre style='color:#555'>> @@ -6,7 +6,7 @@ def self.coder
   def set_title(title = nil)
     if title
       @title = TitleHelper.coder.decode(title.gsub("<bdi>", "\u202a").gsub("</bdi>", "\u202c"))
-      response.headers["X-Page-Title"] = ERB::Util.u(@title + " | " + t("layouts.project_name.title"))
+      response.headers["X-Page-Title"] = ERB::Util.u("#{@title} | #{t('layouts.project_name.title')}")
</pre>
<p>This is getting quite messy - might <code>format</code> be a better choice here?</p>

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