Package xim provides quazi‐ monotonically‐increasing unique‐identifiers.
The serialized form of the xim-id is safe to use as a file or directory name.
Online documentation, which includes examples, can be found at: http://godoc.org/github.com/reiver/go-xim
Here is an example of using package xim:
var id xim.ID = xim.Generate()Internally, the xim-id is compactly stored in an uint64. The anatomy of this is as follows:
unix timestamp (39-bits)
▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼
0b0000000001100001100001110110100111011001110000111111000101100100
▲ ▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲
always zero (1-bit) chaos (20-bits)
The xim.ID.UnixTime() method will give you that 39-bit unix timestamp.
And the xim.ID.Chaos() method will give you that 24-bit chaos.
(The chaos is just a randomness that helps make these xim-ids unique, when multiple xim-ids are being produced simultaneously.)
On thing to note that is, because this puts the unix timestamp at the most-significant-bits, that the numerical-ordering of this uint64 will almost always be the same as temporal-ordering.
This was done intentionally.
This is serialized using what this package calls xim notation. An example of xim notation looks like this:
xi-556PVvNyq3m
The anatomy of the xim string is as follows:
a special base64 encoding
▼▼▼▼▼▼▼▼▼▼▼
xi-556PVvNyq3m
▲▲ ▲
prefix suffix
So every xim string starts with the characters xi, and ends with the character m.
And then what is in the middle of those is a special base64 encoding of the uint64 mentioned before.
What is special about the base64 encoding is that it doesn't use the usual ordering of the symbols. This special base64 encoding uses:
┌───────┬────────┬──────┐
│ Index │ Binary │ Char │
├───────┼────────┼──────┤
│ 0 │ 000000 │ - │
├───────┼────────┼──────┤
│ 1 │ 000001 │ 0 │
├───────┼────────┼──────┤
│ 2 │ 000010 │ 1 │
├───────┼────────┼──────┤
│ 3 │ 000011 │ 2 │
├───────┼────────┼──────┤
│ 4 │ 000100 │ 3 │
├───────┼────────┼──────┤
│ 5 │ 000101 │ 4 │
├───────┼────────┼──────┤
│ 6 │ 000110 │ 5 │
├───────┼────────┼──────┤
│ 7 │ 000111 │ 6 │
├───────┼────────┼──────┤
│ 8 │ 001000 │ 7 │
├───────┼────────┼──────┤
│ 9 │ 001001 │ 8 │
├───────┼────────┼──────┤
│ 10 │ 001010 │ 9 │
├───────┼────────┼──────┤
│ 11 │ 001011 │ A │
├───────┼────────┼──────┤
│ 12 │ 001100 │ B │
├───────┼────────┼──────┤
│ 13 │ 001101 │ C │
├───────┼────────┼──────┤
│ 14 │ 001110 │ D │
├───────┼────────┼──────┤
│ 15 │ 001111 │ E │
├───────┼────────┼──────┤
│ 16 │ 010000 │ F │
├───────┼────────┼──────┤
│ 17 │ 010001 │ G │
├───────┼────────┼──────┤
│ 18 │ 010010 │ H │
├───────┼────────┼──────┤
│ 19 │ 010011 │ I │
├───────┼────────┼──────┤
│ 20 │ 010100 │ J │
├───────┼────────┼──────┤
│ 21 │ 010101 │ K │
├───────┼────────┼──────┤
│ 22 │ 010110 │ L │
├───────┼────────┼──────┤
│ 23 │ 010111 │ M │
├───────┼────────┼──────┤
│ 24 │ 011000 │ N │
├───────┼────────┼──────┤
│ 25 │ 011001 │ O │
├───────┼────────┼──────┤
│ 26 │ 011010 │ P │
├───────┼────────┼──────┤
│ 27 │ 011011 │ Q │
├───────┼────────┼──────┤
│ 28 │ 011100 │ R │
├───────┼────────┼──────┤
│ 29 │ 011101 │ S │
├───────┼────────┼──────┤
│ 30 │ 011110 │ T │
├───────┼────────┼──────┤
│ 31 │ 011111 │ U │
├───────┼────────┼──────┤
│ 32 │ 100000 │ V │
├───────┼────────┼──────┤
│ 33 │ 100001 │ W │
├───────┼────────┼──────┤
│ 34 │ 100010 │ X │
├───────┼────────┼──────┤
│ 35 │ 100011 │ Y │
├───────┼────────┼──────┤
│ 36 │ 100100 │ Z │
├───────┼────────┼──────┤
│ 37 │ 100101 │ _ │
├───────┼────────┼──────┤
│ 38 │ 100110 │ a │
├───────┼────────┼──────┤
│ 39 │ 100111 │ b │
├───────┼────────┼──────┤
│ 40 │ 101000 │ c │
├───────┼────────┼──────┤
│ 41 │ 101001 │ d │
├───────┼────────┼──────┤
│ 42 │ 101010 │ e │
├───────┼────────┼──────┤
│ 43 │ 101011 │ f │
├───────┼────────┼──────┤
│ 44 │ 101100 │ g │
├───────┼────────┼──────┤
│ 45 │ 101101 │ h │
├───────┼────────┼──────┤
│ 46 │ 101110 │ i │
├───────┼────────┼──────┤
│ 47 │ 101111 │ j │
├───────┼────────┼──────┤
│ 48 │ 110000 │ k │
├───────┼────────┼──────┤
│ 49 │ 110001 │ l │
├───────┼────────┼──────┤
│ 50 │ 110010 │ m │
├───────┼────────┼──────┤
│ 51 │ 110011 │ n │
├───────┼────────┼──────┤
│ 52 │ 110100 │ o │
├───────┼────────┼──────┤
│ 53 │ 110101 │ p │
├───────┼────────┼──────┤
│ 54 │ 110110 │ q │
├───────┼────────┼──────┤
│ 55 │ 110111 │ r │
├───────┼────────┼──────┤
│ 56 │ 111000 │ s │
├───────┼────────┼──────┤
│ 57 │ 111001 │ t │
├───────┼────────┼──────┤
│ 58 │ 111010 │ u │
├───────┼────────┼──────┤
│ 59 │ 111011 │ v │
├───────┼────────┼──────┤
│ 60 │ 111100 │ w │
├───────┼────────┼──────┤
│ 61 │ 111101 │ x │
├───────┼────────┼──────┤
│ 62 │ 111110 │ y │
├───────┼────────┼──────┤
│ 63 │ 111111 │ z │
└───────┴────────┴──────┘
The advantage of this is that lexical-ordering (in Unicode & ASCII) is also symbol-ordering.
One design goal is that lexical ordering of the xim strings is (almost always) also temporal ordering of the xim strings.
Another design goal of it is that these xim strings should be able to be used as a file-name, or a directory-name.
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