aptos-move-language

Abilities—copy, drop, store, and key—are Move type annotations that govern whether structs can be copied, discarded, stored globally, or used as resource keys. Apply abilities at struct definition to enforce safety rules; key ability marks resources storable in global state, while copy and drop enable implicit operations. This design prevents accidental loss of linear assets and ensures type-safe resource management on Aptos.

Phantom types are generic parameters that appear in struct declarations but not in field definitions—they exist purely for type-checking. Use phantom types to attach metadata or constraints to structs without storing actual data, enabling compile-time validation without runtime overhead. Common in Move for marking capabilities or linking abstract properties to concrete resources on Aptos.

Use move_to to store a resource in an account's global storage and borrow_global to retrieve immutable or mutable references to it. move_to requires the signer to authorize the operation; borrow_global requires the account address and resource type. These operations are linear-safe; borrowed references prevent simultaneous exclusive access, protecting asset integrity in Aptos smart contracts.

References (&T and &mut T) allow temporary, non-owning access to values without moving them. Ownership transfers happen only when passing values directly. Move's strict rules prevent simultaneous mutable access and enforce that resources cannot be implicitly copied or dropped, making references essential for safe shared access patterns in Aptos contracts without losing linear guarantees.

A signer is a special Move type representing a verified transaction sender; only entry functions can receive signer parameters, which are never stored. Use signers to authorize operations like move_to, ensuring transactions come from legitimate accounts. Signer patterns gate access to sensitive functions and prove account ownership without storing credentials, core to Aptos transaction security.

Move uses public, public(friend), and private visibility. Public functions are callable externally; public(friend) functions are restricted to modules declared as friends; private functions are internal only. Use friend declarations to share implementation details between related modules while blocking external access. Visibility controls encapsulation and prevents unauthorized asset manipulation in Aptos deployments.