The Go standard library. At least two things coming together: A stripped down language, that explicitly aims to be readable and experienced programmers / authors.
Example: The Sum method of the hash.Hash interface takes a byte slice as an argument, and appends the hash to it. Why not take zero arguments and simply return a new slice? Because the authors recognized that if you're doing hashing, you probably care about performance. Appending to a supplied slice allows you to save an allocation.
The stdlib is full of little details like that, and it adds up to a really great programming experience. Go may be lacking in some respects, but it has Good Design stamped all over it.
I worked with Rob on that library and that's really not the case. It was designed from the ground up to replace the existing template library which was bad in several ways. The parser (which is I think what you refer to) is just an implementation detail.
Right, but why can't I call define custom operators? And why is there no bracketing in conditionals? It just feels clunky to me (but maybe I'm too spoiled with Jinja2). I still feel like you could allow execution of functions passed in the data argument (as long as the developer doesn't shoot themselves in the foot, it shouldn't be a security problem).
It's stuff like that which makes me feel like it was a PoC (or at least, not designed to be feature-complete). Still, it works pretty well for plenty of usecases (I use to generate config files every once in a while).
I don't recally anyone asking for this before. File an issue? https://golang.org/issue/new
> It's stuff like that which makes me feel like it was a PoC (or at least, not designed to be feature-complete).
It's designed to be a useful template engine. I don't know about "feature complete", but we are still improving it. If you find it lacking then please file issues so that we can think about improving it.