Open Radar

 
Summary:
Apologies for the narrative form of this summary, but I can't come up with a better way to phrase it. 

My application is parsing a binary file format. Certain data structures in this file include a one byte tag, which can take one of a small number (approx. 9) values. This seems like the perfect use of a Swift enum. Great, let's do it:

enum Tag : ... {...}
}

According to the documentation, all these single-byte values are ASCII characters. All right, let's make Tag a Character, and set the first value. 
enum Tag : Character { Byte = "B" }
Testing the size of the Tag with 
sizeof(Tag.RawValue.self)
reveals that this enum is 9 bytes! That's huge! And we don't have 9 bytes of data to read in anyway, since our field is 1 byte. So let's make it a UInt8 instead:
enum Tag: UInt8 {Byte = "B"}
error: "'String' is not convertible to 'UInt8'"
All right, let's try a character literal B
enum Tag: UInt8 {Byte = 'B'}
error: invalid character in source file. 

To make a long story short, there appears to be no way to work around this such that the B appears anywhere in the source code (except in a comment). The only way to make this work is to use 
enum Tag: UInt8 { Byte = 0x42} // or 66
This is not acceptable from a language that purports to be a general purpose programming language, usable for systems programming in particular.

Steps to Reproduce:
1. Install Xcode 7b2
2. Create a new playground.
3. Paste the following code:

enum Tag : UInt8 {
    case Byte = 'B'
    case Char = 'C'
    case Double = 'D'
}

enum Tag2 : UInt8 {
    case Byte = "B"
    case Char = "C"
    case Double = "D"
}

enum Tag3 : UInt8 {
    case Byte = UInt8(ascii:"B")
    case Char = UInt8(ascii:"C")
    case Double = UInt8(ascii:"D")
}


Expected Results:
At least one of the enums should successfully compile. I don't really care which one, but as it is, the only ones that will compile are:

enum Tag4 : UInt8 {
    case Byte = 0x42
    case Char = 0x43
    case Double = 0x44
}

enum Tag5 : UInt8 {
    case Byte = 66
    case Char = 67
    case Double = 68
}


Actual Results:
Tag:
error: invalid character in source file.

Tag2:
error: String is not convertible to 'UInt8'

Tag3: 
error: Raw value for enum case must be a literal

Version:
Version 7.0 beta (7A121l)
OS X 10.10.4 (14E46)

Notes:


Configuration:


Attachments: