[swift-evolution] Make integer conversion initializers failable

[Xiaodi Wu]

I could get behind this iff there's no performance impact. Otherwise,
I'd rather have the option to write a function than not have the
option of a performant conversion.

On Fri, Feb 12, 2016 at 12:10 PM, Félix Cloutier
<swift-evolution at swift.org> wrote:
> My use case is a small chess game where my Board class has a Location
> indexer, and any Location object has a guaranteed value on the Board. The
> Location struct handles adding signed deltas to coordinates and returns nil
> when that location wouldn't exist. My coordinates are UInt8 values and the
> "casting" code looks like:
>
> private func intToU8(int: Int) -> UInt8? {
> if int >= 0 && int <= Int(UInt8.max) {
> return UInt8(int)
> }
> return nil
> }
>
> Of course, if UInt8's initializer returned an Optional instead of trapping,
> I wouldn't need that function at all.
>
> In general, I would also say that it's a good idea to make dangerous
> behavior explicit. I think that Swift's model for converting integers is
> already punishing enough that we might as well add the exclamation mark.
>
> Félix
>
> Le 12 févr. 2016 à 12:27:55, Javier Soto <javier.api at gmail.com> a écrit :
>
> I'm curious: how would you use the failable initializers? I feel like, more
> often than not, you would end up force-unwrapping the return value, which
> would produce the same result as trapping inside. But I guess in that case
> you would make it clearer on the caller site that that can fail?
> On Fri, Feb 12, 2016 at 9:23 AM Félix Cloutier <swift-evolution at swift.org>
> wrote:
>>
>> It appears that the current integer conversion initializers will either
>> always work, possibly trap, or truncate:
>>
>> init(_: Int)
>> init(_: Int8)
>> init(_: Int16)
>> init(_: Int32)
>> init(_: Int64)
>> init(_: UInt)
>> init(_: UInt8)
>> init(_: UInt16)
>> init(_: UInt32)
>> init(_: UInt64)
>> init(truncatingBitPattern: Int)
>> init(truncatingBitPattern: Int16)
>> init(truncatingBitPattern: Int32)
>> init(truncatingBitPattern: Int64)
>> init(truncatingBitPattern: UInt)
>> init(truncatingBitPattern: UInt16)
>> init(truncatingBitPattern: UInt32)
>> init(truncatingBitPattern: UInt64)
>>
>>
>> I suggest that we change trapping initializers to failable initializers.
>> Initializers that can't fail (identity, unsigned -> bigger signed/unsigned,
>> signed -> bigger signed) should keep a non-Optional type.
>>
>> This could extend to changing SignedIntegerType's and
>> UnsignedIntegerType's (U)IntMax to failable initializers as well.
>>
>> I think I remember someone on the core team saying that someone's working
>> on integer types at the moment. Is that right?
>>
>> Félix
>>
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>
> --
> Javier Soto
>
>
>
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