I tried (lightly) to convince people to switch from <> to [] well before Rust 1.0, but even when many (not sure if it was most) agreed that square brackets were superior, there was no will to make such a radical syntactic change, for two main reasons:
1. Angle brackets are also not uniformly superior. Technically, I think it’s fair to consider them uniformly superior, but social aspects are important too; there was reasonable concern that Rust had exhausted its weirdness budget. (Of the most common languages people may be familiar with when coming to Rust, I think Scala is the only one that uses square brackets for generics; the likes of C++, C and Java are much more common and use angle brackets.)
2. For Rust specifically, it wouldn’t actually have been just a syntactic change—if you want to change array indexing to use function call syntax, you’ve got to sort out more technical challenges there, things that would be approaching trivial in full-GC languages but which are actually rather difficult in Rust. Specifically, function calls are rvalues only (`… = f()`), but array indexing can be an lvalue also (`a[i] = …`). So you need to more or less unify the Index and Fn trait families, auto-ref/-deref might cause trouble, and placement might make an appearance in it too for best results (and that’s something that still isn’t resolved). Now I’m inclined to believe that these changes would have been a really good thing and resulted in a more coherent and incidentally slightly more flexible language (and not in a dangerous way), but it would now be even more difficult to achieve (though not impossible; the edition system could be used for the syntax side of things, and Fn/Index implementations are still mutually exclusive, because you can’t implement Fn manually on stable, so you could blanket-impl Fn traits for types implementing Index traits without breaking backwards-compatibility).
I’m simplifying the story a bit. Others may fill out more history and technical detail if they desire. I’m going to bed.
1. Angle brackets are also not uniformly superior. Technically, I think it’s fair to consider them uniformly superior, but social aspects are important too; there was reasonable concern that Rust had exhausted its weirdness budget. (Of the most common languages people may be familiar with when coming to Rust, I think Scala is the only one that uses square brackets for generics; the likes of C++, C and Java are much more common and use angle brackets.)
2. For Rust specifically, it wouldn’t actually have been just a syntactic change—if you want to change array indexing to use function call syntax, you’ve got to sort out more technical challenges there, things that would be approaching trivial in full-GC languages but which are actually rather difficult in Rust. Specifically, function calls are rvalues only (`… = f()`), but array indexing can be an lvalue also (`a[i] = …`). So you need to more or less unify the Index and Fn trait families, auto-ref/-deref might cause trouble, and placement might make an appearance in it too for best results (and that’s something that still isn’t resolved). Now I’m inclined to believe that these changes would have been a really good thing and resulted in a more coherent and incidentally slightly more flexible language (and not in a dangerous way), but it would now be even more difficult to achieve (though not impossible; the edition system could be used for the syntax side of things, and Fn/Index implementations are still mutually exclusive, because you can’t implement Fn manually on stable, so you could blanket-impl Fn traits for types implementing Index traits without breaking backwards-compatibility).
I’m simplifying the story a bit. Others may fill out more history and technical detail if they desire. I’m going to bed.