On 01.06.2016 11:00, Austin Zheng wrote:
Tuples are a structural type, they are described entirely by the fact
that they are a tuple, plus their contained types.
Enum cases are not individual types; that precedent exists nowhere in
Swift. You can't (yet) build a structural type out of something that
isn't a type. The fact that you had to propose something like
"AdhocEnumFitFill_2383748" as an autogenerated name for the type
demonstrates the proposal's weaknesses: a tuple is an ad-hoc type that
describes itself, while an anonymous enum isn't.
Yes, I understand the point about the type of such adhoc enum.
The only workaround I can see in this case(if we'd really want to have it
in language) if adhoc enum type will be `(.Fit|.Fill)` i.e. textual
representation if the declared type. As I understand this also could not be
a solution.. I.e. for example `(Int,String,(.Fit|.Fill))->String`
From other point of view, adding such type to typesystem will add some
consistence : you can create a function that don't need definition of
separate structure type(tuple will be used) and don't need separate enum
type(ad-hoc enum will be used). I.e. all data the function needs to process
could be described in function definition. Today we need to use ugly Bool
flags in case we want to achieve the same target.
Now if enum cases were equivalent if they had the same name (like how
"Int" means the same thing no matter what tuple or generic type it is
used in), we'd have a good foundation for a self-describing structural
type. But this isn't how the existing named enum types work. Why would
it be a good idea to make anonymous enum cases interchangeable by name?
Properties on different types aren't interchangeable, even if they have
the same type. In fact, no type member that I am aware of is
interchangeable solely on the basis of name. An "ArtistAction.Draw" and
"CowboyAction.Draw" might have the same name, but they mean completely
different things.
I don't think they should be 'interchangeable by name', but just like
tuples if you defined adhoc enum with exactly the same cases as ad-hoc enum
in function parameters - then they are of the same type.
I.e. :
func foo(option: (.fit|.fill)) {..}
foo(.fit) // .fit is of type (.fit|.fill) from definition
let e : (.fit|.fill) = .fit
foo(e) // e is of (.fit|.fill) type, equal to definition
but
func foo2(option: (.fit|.fill|.other)) {..}
foo2(.fit) // ok, here .fit is of (.fit|.fill|.other) type
foo2(e) --> Error, e is not of type (.fit|.fill|.other)
Finally, I have to ask: if you are updating your anonymous enum in
multiple places, how much effort have you actually saved over a one-line
enum definition? In fact, tuples are a great example of this: best
practices usually state that they are good for ad-hoc destructuring,
such as retrieving multiple return values from a function or pattern
matching across several values at once, but structs are better used for
almost everything else, since they carry semantic meaning that tuples
don't.
Just the same pros and cons for ad-hoc enums vs enum declaration as for
tuples vs struct declaration. Yes can use it with care and you can use it
in wrong way.
Btw, I feel like this could be very handy to return adhoc enum:
func something() -> (.one|.two|.three) {...}
I hope that clarifies my thoughts on the matter.
Best, Austin
On Jun 1, 2016, at 12:36 AM, Vladimir.S <[email protected]> wrote:
On 01.06.2016 9:55, Austin Zheng via swift-evolution wrote:
Maybe it's overkill. My personal opinion is that breaking the
symmetry of the language like this (are there any other types of
function arguments that cannot be passed as either variable values
or literals?) is too much a price to pay. Your library thinks it's
being clever and vends its functions as taking anonymous enum flags,
and now there are a bunch of things I can't do with those functions
anymore.
A regular enum can be declared in one line anyways:
enum ScaleCropMode { case Fit, Fill }
Why do we have tuples? Struct could be defined by one line `struct
SomeValue { var x = 0, y = 0 }` ;-) I.e. from my point of view
developer should decide what he/she wants to use: ad-hoc enum or
defined enum type *exactly* as now he/she can decide to use the same
tuples in multiply functions instead of one defined struct type.
I replied regarding the variable on other message. (In short: I think
of the same principle as for tuples: you can declare variable `let e:
(.fill | .fit) = .fill` and use it)
Austin
On May 31, 2016, at 11:44 PM, Charles Constant
<[email protected] <mailto:[email protected]>> wrote:
It breaks the ability to pass in a variable containing the
desired
value, rather than the literal value itself.
Maybe that's appropriate? If the caller is not passing in a
hardcoded enum case, then that enum is probably general enough
that it warrants a normal enum. But there are also situations
where the same function is called from several files in the same
code-base with different flags. Those are situations where it
feels like overkill to clutter up my codebase with separate enums,
only used by a single function.
On Tue, May 31, 2016 at 9:24 PM, Austin Zheng via swift-evolution
<[email protected] <mailto:[email protected]>>
wrote:
I admire the desire of this proposal to increase the readability
of code. I'm -1 to the proposal itself, though:
- It breaks the ability to pass in a variable containing the
desired value, rather than the literal value itself. (Unless you
actually want a not-so-anonymous enum type whose definition
happens to live in a function signature rather than somewhere
you'd usually expect a type definition to live.) - It breaks the
ability to store a reference to the function in a variable of
function type (ditto). - Almost every time I've wanted to use one
of these "anonymous enums" in my code, I've ended up needing to
use that same enum elsewhere. In my experience, 'lightweight
enums' don't end up saving much time compared to a full-fledged
one.
Like Brent said, I have to say no to any proposal that tries to
make enums synonyms for numerical values. What happens if you
rearrange your anonymous enum cases between library versions? Do
you somehow store an opaque case-to-UInt8 table somewhere for
every anonymous enum you define for resilience? What happens when
people start bringing back terrible C patterns, like doing
arithmetic or bitwise ops on the underlying case values? At least
you have to try pretty hard as it is to abuse Swift's enums.
Austin
On Tue, May 31, 2016 at 8:25 PM, Brent Royal-Gordon via
swift-evolution <[email protected]
<mailto:[email protected]>> wrote:
And the obvious answer is you can have up to 255 of these babies
for the anonymous enum type, and be able to pass numerical
equivalents UInt8 with compile time substitution. That the
ad-hoc enumeration is basically a syntactic shorthand for UInt8,
with an enforced upper bound compile time check simplifies
everything including switch statements.
If I wanted a language like that, I'd be writing C, not Swift.
-- Brent Royal-Gordon Architechies
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