Pair

Pairs of values are specified using the type Pair t1 t2, where t1 and t2 are types. Pairs are considered ADT's.

Take the below example, we have a library function called build_pair which takes two parameters, a ByStr20 and a String, then creates a Pair of those values in the constructor declaration {ByStr20 String} . This is called in the public transition Mint where input_pair is of type Pair. The procedure Minting takes a Pair of ByStr20 String and then uses PairUtils to be able to use @fst and @snd to retrieve the first and second value from the Pair.

import PairUtils
let build_pair =  fun (input_to_address : ByStr20) =>  fun (input_token_uri : String) =>    Pair {ByStr20 String} input_to_address input_token_uri
...
transition Mint(to: ByStr20, token_uri: String)  input_pair = build_pair to token_uri;  Minting input_pair;  ...end
procedure Minting(input_pair: Pair ByStr20 String)  to = let fst_string_bystr20 = @fst ByStr20 String in    fst_string_bystr20 input_pair;  token_uri = let snd_string_bystr20 = @snd ByStr20 String in    snd_string_bystr20 input_pair;  ...end

Consider the below example of BatchMint, it takes a single address, and a list of token URI's. pair_token_uri_list is defined as a (Pair ByStr20 String), tmp_func is a temporary function to create the list and stores to. input_list then constructs, the empty Map of Pairs, the temporary function with the address, and then the List of Strings, resulting in a full map of a single address of ByStr20 and multiple uri's of type String. Now with a list of Pairs, these can be iterated over and passed to the procedure as a single Pair.

transition BatchMint(to: ByStr20, token_uris_list: List String)  pair_token_uri_list = @list_map String (Pair ByStr20 String);  tmp_fun = build_pair to;  input_list = pair_token_uri_list tmp_fun token_uris_list;  forall input_list Minting;

Further reading#