In The Sad Tragedy of Micro-Optimization Theater we discussed the performance considerations of building a fragment of HTML
string s =
@"<div class=""action-time"">{0}{1}</div>
<div class=""gravatar32"">{2}</div>
<div class=""details"">{3}<br/>{4}</div>";
return String.Format(s, st(), st(), st(), st());
The second act of this particular theater was foreshadowed by Stephen Touset's comment:
The correct answer is that if you're concatenating HTML, you're doing it wrong in the first place.
Use an HTML templating languageThe people maintaining your code after you will thank you (currently, you risk anything from open mockery to significant property damage)
The performance characteristics of building small string fragments isn't just a red herring -- no, it's far, far worse.
The entire question is wrongThis is one of my favorite lessons from The Pragmatic Programmer
When faced with an impossible problem, identify the real constraintsAsk yourself: "Does it have to be done this way? Does it have to be done at all?"
If our ultimate conclusion was that performance is secondary to readability of code, that's exactly what we should have asked, before doing anything else.
Let's express the same code sample using the standard ASP.NET MVC templating engineAnd yes, we render stuff like this all over the place in Stack OverflowIt's the default method of rendering for a reason.
<div class="action-time"><%= User.ActionTime %></div>
<div class="gravatar32"><%= User.Gravatar %></div>
<div class="details"><%= User.Details %><br/><%= User.Stuff %></div>
We have a HTML file, through which we poke some holes and insert the data.
Simple enough, and conceptually similar to the String.Replace versionTemplating works reasonably well in the trivial cases when you have an object with obvious, basic data types in fields that you spit out.
But beyond those simple cases, it's shocking how hairy HTML templating getsWhat if you need do to a bit of formatting or processing to get that data into shape before displaying it? What if you need to make decisions and display things differently depending on the contents of those fields? Your once-simple page templates get progressively more and more complex.
<%foreach (var User in Users) { %>
<div class="action-time"><%= ActionSpan(User)%></div>
<% if (User.IsAnonymous) { %>
<div class="gravatar32"><%= RenderGravatar(User)%></div>
<div class="details"><%= RepSpan(User)%><br/><%= Flair(User)%></div>
<% } else { %>
<div class="anon">anonymous</div>
<% } %>
<% } %>
This is a fairly mild case, but you can see where templating naturally tends toward a frantic, unreadable mish-mash of code and template -- Web Development as Tag Soup.
If your HTML templates can't be kept simple, they're not a heck of a lot better than the procedural string building code they're replacingAnd this is not an easy thing to stay on top of, in my experience.
The daily grind of struggling to keep the templates from devolving into tag soup starts to feel every bit as grotty as all that nasty string work we were theoretically replacing
Now it's my turn to ask -- why?
I think existing templating solutions are going about this completely backwards.
Rather than poking holes in HTML to insert code, we should simply treat HTML as code
Like so:
foreach (var User in Users)
{
<div class="action-time">[ActionSpan(User)]</div>
if (User.IsAnonymous)
{
<div class="gravatar32">[RenderGravatar(User)]</div>
<div class="details">[UserRepSpan(User)]<br/>[UserFlairSpan(User)]</div>
}
else
{
<div class="anon">anonymous</div>
}
}
Seamlessly mixing code and HTML, using a minumum of those headache-inducing escape characters.
Is this a programming language for a race of futuristic supermen? NoThere are languages that can do this right now, today -- where you can stick HTML in the middle of your codeIt's already possible using Visual Basic XML Literals, for example.
Even the hilariously maligned X# has the right core ideaTemplating tends to break down because it forces you to treat code and markup as two different and fundamentally incompatible thingsWe spend all our time awkwardly switching between markup-land and code-land using escape sequences.
They're always fighting each other -- and us
Seeing HTML and code get equal treatment in my IDE makes me realize one thing:
We've all been doing it wrong
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