> On 30 May 2017, at 16:27, David Sweeris via swift-evolution
> <swift-evolution@swift.org> wrote:
>
> On May 30, 2017, at 03:25, Pavol Vaskovic <p...@pali.sk
> <mailto:p...@pali.sk>> wrote:
>
>> On Tue, May 30, 2017 at 7:51 AM, David Sweeris <daveswee...@mac.com
>> <mailto:daveswee...@mac.com>> wrote:
>>
>> `(Int, Int, Int, Int)` isn't *that* horrible compared to "[Int x 4]", but
>> would you want to replace "[Int8 x 10000]" with the multipage-long tuple
>> equivalent?
>>
>> 😳
>> It would be really helpful to my understanding, if you spoke about a
>> practical use case. This reads as a contrived counterexample to me…
>>
>> If your type really has 10 000 values in it, why does it have to be static,
>> why doesn't normal Array fit the bill?
>
> Sure, I meant it as an example of how unwieldy large tuples can be. Even
> medium ones, really. Tuples are great for bundling a few values, but much
> more than that any they become annoying to work with because there's no easy
> way to iterate through them. As a more realistic example, what if you want a
> stack-allocated 256-element buffer (which is a real possibility since
> statically-allocated C arrays are imported as tuples)? You have to manually
> keep track of i, because you have to hard-code which element you're
> addressing ("buf.0", "buf.1", etc), rather than being able to look it up
> directly from an index variable like, well, an array ("buf[i]").
The other issue is when you're importing an existing enum from a fixed size
data structure which has a fixed array count:
// in include/*.h
#define MAX_ELEMENTS 100
typedef struct {
size_t count;
int elements[MAX_ELEMENTS];
} MyData
This gets imported into Swift as a 100-element tuple, which means you can't do
elements[i] to look them up. And while a case statement will be hand-rollable,
given that this is a compile-time value which could be changed in the future,
it won't be safe.
You can end up with such unrolled loops (e.g.
https://github.com/apple/swift-corelibs-foundation/blob/46b4e84a263d4fb657d84dfa4ca5b8fb4ed1f75f/Foundation/NSDecimal.swift#L1546-L1591
<https://github.com/apple/swift-corelibs-foundation/blob/46b4e84a263d4fb657d84dfa4ca5b8fb4ed1f75f/Foundation/NSDecimal.swift#L1546-L1591>
) but they're pretty unwieldy for something that should be a compile-time
check.
It can be hacked with mirror, but well, it's a hack:
subscript(index:Int) -> Int {
let all = Mirror(reflecting:self.elements).children.map({$0.value as!
Int})
return all[index]
}
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