There's nothing preventing UFCS from working with code completion. e.g. given:

    int addOne(int v){
        return v+1;
    }

You can now write code like this:

    int foo=3;
    writeln(foo.addOne);

There is absolutely no reason that typing "foo." would not suggest "addOne" as possibility.

My comment was about the reverse, using function syntax for methods.

Furthermore, I don’t think it necessarily makes sense for all functions that happen to take, say, a string as their first argument, to be listed in the code completion for method invocation on a string variable.

If you merely want to define auxiliary methods outside of a class, which is the thing the GP seems to like, that’s what’s usually called “extension methods”. It doesn’t require uniform call syntax.

> using function syntax for methods

hmm, yeah fair enough I suppose. I don't think I've found a good use-case for that yet. I guess having the symmetry there makes the feature easier to explain at least? I dunno.

> Furthermore, I don’t think it necessarily makes sense for all functions that happen to take, say, a string as their first argument, to be listed in the code completion for method invocation on a string variable.

All functions in scope that happen to take a string as their first argument. If this turns into an actual problem in practice it's quite doable to refactor things such that it's not an issue.

I find that when I use autocomplete I'll be typing the first bit of the method name in any case. I never "browse" autocomplete to look for the thing I need.

Extension methods are another way to do the same thing yes, but that feels like special-casing behavior, where UFCS is more general. With extension methods you need to think of how to implement it wrt things that don't usually have methods attached. With UFCS that just works the way you'd expect it to.

I agree with this. I'd go even further and say that dot syntax should only be used to access things that are /actually a part of the object/, whether record fields or methods. If you use the dot for everything just because it's convenient, you're making the code structure harder to understand by syntactically conflating different mechanisms.

I use it when the idea is data flows from left to right.

unless your intent is to simulate open classes, and the functions you call via the dot are conceptually meant to be an extended set of methods for the type