The mathematical structure of a set is an unordered collection. If a set does not have an order, how are they serialized by the PACK instruction?
According to this overview set is packable.
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1 Answer
Sets are serialized by first ordering the elements, and then packing them as a sequence which is also how lists are represented when PACK is called. This means that these two expressions evaluate to the same, since they are first sorted, and then serialized.
ligo interpret -s pascaligo 'Bytes.pack(set [ 1; 2; 3; 4 ])'
ligo interpret -s pascaligo 'Bytes.pack(set [ 4; 2; 3; 1 ])'
Both output the same byte array
0x0502000000080001000200030004
Where
05is the prefix for any output from thePACKinstruction02is the tag for the sequence type00000008is the four bytes indicating the size of the coming values, in bytes0001000200030004are then numbers1,2,3,4encoded with first a00tag to indicate that this is a integer, and the numbers01, ...04are the encoding of the actual numbers.
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2Note also, that in Michelson (may be different in Ligo), concrete sets must always be ordered. That is,
PUSH (set nat) { 1 ; 3 ; 2 };does not typecheck, where asPUSH (set nat) { 1 ; 2 ; 3 };does.– arvidjOct 15, 2020 at 14:48 -
For more details on how integers are encoded: tezos.stackexchange.com/a/2882/5135 Oct 15, 2020 at 20:21
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Each datatype that is
Comparablehas an order. The ordering of integers is there numerical order, the ordering of strings and addresses is alphabetical ordering. Cf michelson.nomadic-labs.com/#instr-COMPARE Oct 16, 2020 at 13:47