Anonymous Structs

[anandabits (Matthew Johnson)]

@cukr

Would you be able to make an anonymous struct, without putting it in a protocol type, and access the properties of it?

let a = {[x = 1, y = 1]}
print(a.x)

I don't think so. If this was supported it would have to be equivalent to some Any. But no protocol conformances would be synthesized so the only way you could do anything with this type would be to use reflection to access the stored properties. I can't think of any good use cases for that.

@cukr

What if you have more than one anonymous struct, but in a single expression? Would it just complain that I try to put two different types as keys in a single dict?

var d = [
    {[x = 1, y = 1]}: "Hello",
    {[x = 2, y = 2]}: "World",
]

You left off the type annotation on the dictionary here, which would be necessary with anonymous structs. As @Nickolas_Pohilets mentioned, each anonymous struct would be a distinct type. So you would need to use an existential type context. In a hypothetical future version of Swift would would be able to do this:

var d: [any Hashable: String] = [
    {[x = 1, y = 1]}: "Hello",
    {[x = 2, y = 2]}: "World",
]

@cukr

I was just wondering if anonymous structs would be as powerful as structs. It seems they won't be. There will be a lot of situations where you will be forced to use normal structs. In contrast the only place that you're unable to use anonymous functions is when you want to have argument labels (and it could be fixed in the future) Thanks for the answers!

The primary limitations of anonymous structs relative to nominals structs are that you can't name the type and they therefore can't be instantiated directly (or more generally, static members can't be used directly). They are only instantiated at the point of the anonymous struct expression, code contained in that expression which uses Self to name the type, and in generic code which uses initializer requirements. Similarly, static members are only usable in code contained in the anonymous struct expression or in generic code which uses the static member requirements.