Move 2.0 Language Release

The Move 2.0 language release adds a number of new features to Move. The documentation of those features is integrated into the book, and marked in text with “Since language version 2.0”. This section gives an overview of the new features and links to the documentation:

• 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 to access elements of vectors and of resource storage with notations like &mut vector[index], or &mut Resource[addr], respectively.

• Positional Structs allow to define wrapper types such as struct Wrapped(u64). Positional structs are described here. Enum variants are also allowed to be positional.

• Dot-dot pattern wildcards enable statements like let Struct{x, ..} = value to match selective parts of data. They are described here. Those patterns are also allowed for enum variants.

• Package visibility allows to declare 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 simply 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 also here.

• New Cast Syntax Until now, casts had to always be in parentheses, requiring code like function((x as u256)). This requirement is now dropped and casts can be top-level expressions without parenthesis, 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.