Skip to main content

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#

Scilla Documentation - Pair