How to add cycles on canister creation?

qwertytrewq · September 10, 2023, 10:52pm

How to add cycles on canister creation (constructor call by Motoko)?

ChatGPT claims “Motoko, the programming language for the DFINITY Internet Computer, does not provide a direct mechanism within the code to add or allocate cycles during the creation of a canister.”

To function calls cycles are added by pairing Cycles.add and Cycles.accept. But, apparently, Cycles.accept can’t be run from actor creation code. So, how to do this?

qwertytrewq · September 10, 2023, 11:11pm

Accordingly ChatGPT, “As of my last knowledge update in September 2021, when you create a new canister on the DFINITY Internet Computer using Motoko code, the amount of cycles allocated to the canister is determined by the settings provided in your deployment configuration. This configuration is typically specified using the DFX (Dfinity eXtended) tool or the Internet Computer’s governance system, and it’s not directly controlled within the Motoko code.”

So, if the canister is not presented in dfx.json, but is created directly from Motoko code, how is the amount of cycles allocated determined?

claudio · September 12, 2023, 5:38pm

IIRC you just call Cycles.add() before calling the class constructor. These cycles don’t need be accepted explicitly, and are just added to the new canister.

There is an example here:

github.com

dfinity/examples/blob/3f0765f514e5b61bcb7e9aaa5a04a9a67e271c02/motoko/classes/src/map/Map.mo#L31


      
                case null null;
                case (?bucket) await bucket.get(k);
              };
            };
          
            public func put(k : Key, v : Value) : async () {
              let i = k % n;
              let bucket = switch (buckets[i]) {
                case null {
                  // provision next send, i.e. Bucket(n, i), with cycles
                  Cycles.add(cycleShare);
                  let b = await Buckets.Bucket(n, i); // dynamically install a new Bucket
                  buckets[i] := ?b;
                  b;
                };
                case (?bucket) bucket;
              };
              await bucket.put(k, v);
            };
          
          };

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How to add cycles on canister creation?

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