Constructor
A constructor is a mandatory function in every Aleo program. It does not initialize object instances like constructors in OOP languages. It sets the program's upgrade policy: whether the program can be updated after deployment, and if so, by whom and under what conditions.
It runs once during deployment and the rules it sets are immutable. A constructor might declare the program permanently frozen, upgradable by a specific admin address, or requiring multi-signature approval. Users can check a program's upgrade policy before interacting with it. The constructor must be present for the program to compile and deploy.