How to create a generic integer-to-hex function for all Integer types?

Question

I want to create an Integer-to-Hex function for all integer types.

For 1-byte Int8, it returns two letters, eg 0A

For 2-byte Int16, it returns four letters, eg 0A0B

for 8-byte Int64, it returns 16 letters, eg, 0102030405060708

func hex(v: Int) -> String {
    var s = ""
    var i = v
    for _ in 0..<sizeof(Int)*2 {
        s = String(format: "%x", i & 0xF) + s
        i = i >> 4
    }
    return s
}

func hex(v: Int64) -> String {
    var s = ""
    var i = v
    for _ in 0..<sizeof(Int64)*2 {
        s = String(format: "%x", i & 0xF) + s
        i = i >> 4
    }
    return s
}

func hex(v: Int32) -> String {
    var s = ""
    var i = v
    for _ in 0..<sizeof(Int32)*2 {
        s = String(format: "%x", i & 0xF) + s
        i = i >> 4
    }
    return s
}

func hex(v: Int16) -> String {
    var s = ""
    var i = v
    for _ in 0..<sizeof(Int16)*2 {
        s = String(format: "%x", i & 0xF) + s
        i = i >> 4
    }
    return s
}

func hex(v: Int8) -> String {
    var s = ""
    var i = v
    for _ in 0..<sizeof(Int8)*2 {
        s = String(format: "%x", i & 0xF) + s
        i = i >> 4
    }
    return s
}

The above code works fine.

I then tried to create a generic version like this:

func hex<T: IntegerType>(v: T) -> String {
    var s = ""
    var i = v
    for _ in 0..<sizeof(T)*2 {
        s = String(format: "%x", i & 0xF) + s
        i = i >> 4
    }
    return s
}

When compiling this code, I got the error: T is not convertible to Int

What is the correct way to achieve this task?

Answer 1

Very simple solution is to coalesce the input value into IntMax with .toIntMax().:

func hex<T: IntegerType>(v: T) -> String {
    var s = ""
    var i = v.toIntMax()
    for _ in 0..<sizeof(T)*2 {
        s = String(format: "%x", i & 0xF) + s
        i >>= 4
    }
    return s
}

Note: This works with only 0...Int64.max values.

---

But, I would do:

func hex<T: IntegerType>(v: T) -> String {
    return String(format:"%0\(sizeof(T) * 2)x", v.toIntMax())
}

Note: This works with only 0...UInt32.max values.

---

Added: This works with all available integer types/values.

func hex<T:IntegerType>(var v:T) -> String {
    var s = ""
    for _ in 0..<sizeof(T) * 2 {
        s = String(format: "%X", (v & 0xf).toIntMax()) + s
        v /= 16
    }
    return s
}

• .toIntMax() to cast T to concrete integer type.
• / 16 instead of >> 4.