While acknowledging the use case of "the designer who doesn't know how to program" and the desirability in some sense of separating logic from data, if I am going to slam together some HTML as a programmer, with no "non-programmer" designer in sight, I tend to slap together a local version of templates like this if I can't find a good one available. The reason is, if I'm going to mix logic and presentation anyhow, why bother with a template library that is basically an inner-platform, when I can just use the programming language itself? Then you get other integrations as useful, e.g., do you have some concept of interfaces/traits/whatever? Define a useful default representation for something and you can push it straight out in a template. This may not work for large UI elements, but in terms of "hey, here's how you display a Username in general" it can be useful, and it's not like you're stuck with only that way of rendering an object.

Closures, modules, functions, loops or recursion, conditionals, every feature of your programming language just right there, without some large templating library in the way. Debug your templates with the actual debugger. Very high performance with just a bit of care in the API design. Every programmer in your language can pick this up very quickly with hardly any effort and doesn't have to learn yet another complete templating language to start using your project, it's just comparable to picking up an API.

So many advantages... it's just... you have to be programmer if you want to modify the resulting code. Other than that, and I guess the fact you need to implement whatever discipline you may want on your own[1]... but those are a total killer in many cases.

[1]: This approach does not require that you mix presentation and logic, but if you want that separation, you will need to discipline yourself to maintain it. Though I have to admit, 25 years of programming on the web and I'm frankly still unconvinced by this argument, or, at least, unconvinced that it is the absolute most important thing in every context and only a cretinous lunatic would dare mix logic and presentation. It seems to me to be a rule espoused by far more people than it is followed by.

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