Language Versions

The Move 2 language releases are described on this page. The reference documentation of the new features is integrated into the book, and marked in the text with “Since language version 2.n”.

Move 2.4

The Move 2.4 language release adds the following features to Move:

Struct and Enum Visibility Modifiers: Structs and enums can now be declared with public, package, or friend visibility modifiers. This allows external modules to construct, destruct, pattern-match, and access or modify fields of the type, lifting the previous restriction that limited all such operations to the defining module. See the reference docs for structs and enums.
Compositional Specifications for the Move Prover: The Move Specification Language gains a set of compositional constructs supporting higher-order functions, frame conditions, intermediate-state reasoning, and proof guidance. See the reference docs for Behavioral Predicates, Access Specifiers and Frame Conditions, State Labels, Two-State Specification Functions, Proofs and Lemmas, and Specification Inference.

Move 2.3

The Move 2.3 language release adds the following features to Move:

Signed Integer Types: Move now supports i8, i16, i32, i64, i128, and i256 signed integer types. See the reference doc here.
Builtin Constants: Move now supports a number of builtin constants, namely min/max values for integer types (e.g. MAX_U64, MIN_I32), as well as a constant to determine whether code is running in testing mode. See the reference doc here.

Move 2.2

The Move 2.2 language release adds the following features to Move:

Optional Acquires: The acquires annotation on function declarations can be omitted, to be inferred by the compiler.
Function Values: Move now supports function values, which can be passed around as parameters and stored in resources. See the reference doc here.
Comparison Operations: Move now supports comparison operations (<, >, <=, >=) on all types. See the reference doc here.

Move 2.1

The Move 2.1 language release adds the following features to Move:

Compound Assignments: One can now use x += n, x -= n, etc. to combine assignments and arithmetic operations. See the reference doc here for the supported operations.
Loop Labels: One can now use labels for loops and have a break or continue expression refer to those labels. This makes it possible to continue or break outer loops from within nested loops. See the reference doc here.
Underscore function parameters are wildcards, not symbols: Function parameters named _ no longer act like variables: they do not bind a value, and multiple such parameters to a function do not cause a conflict. Using _ in a value expression will yield an error, as it has no value. This makes the behavior of _ more like the wildcard it is in patterns and let expressions, where it does not bind a value.

Move 2.0

The Move 2.0 language release adds the following features to Move:

Enum Types: add the option to define different variants of data layout in one storable type. They are documented in the Enum Type section.
Receiver Style Functions: add the ability to call functions in the familiar notation value.func(arg). They are documented in this section.
Index Notation: allows access to elements of vectors and of resource storage with notations like &mut vector[index] or &mut Resource[addr].
Positional Structs: allow defining wrapper types such as struct Wrapped(u64). Positional structs are described here. Enum variants can also be positional.
Dot-dot pattern wildcards: enable statements like let Struct{x, ..} = value to match selective parts of data. They are described here. These patterns are also allowed for enum variants.
Package visibility: allows declaring a function to be visible anywhere inside, but not outside, a package. Friend functions continue to be supported, although package visibility is in many cases more suitable. As a more concise notation, package and friend functions can be declared as package fun or friend fun, respectively, instead of the longer public(package) fun and public(friend) fun. This feature is documented here.
Assert abort code optional: The assert! macro can now be used with just one argument, omitting the abort code, in which case a default code will be chosen. See here.
New Cast Syntax: Until now, casts always had to be in parentheses, requiring code like function((x as u256)). This requirement is now dropped and casts can be top-level expressions without parentheses, as in function(x as u256). One still needs to write (x as u64) + (y as u64) in expressions. This similarly applies to the new enum variant test, data is VersionedData::V1.
Well-defined evaluation order: The evaluation order in the cases below is now well-defined (these were previously unspecified):
- The (a) arguments to a function call and the (b) operand expressions in a binary operation are both evaluated from left to right.
- Given a “mutate” expression (see mutating through a reference) of the form *lexp = rexp, where lexp is an expression of type &mut T and rexp is an expression of type T, rexp is evaluated first, followed by lexp.
Bug fix for acquires annotation: A function should be annotated with acquires if and only if it accesses a resource using move_from, borrow_global, or borrow_global_mut, either directly or transitively through a call. Otherwise, it is an error. Previously, when the transitive call graph included a cycle, such errors were not reported: this was incorrect behavior. We have now corrected this behavior to report these errors even when the transitive call graph has cycles.