Standard Library

The Move standard library exposes interfaces that implement the following functionality:

Basic operations on vectors.
Option types and operations onOption types.
A common error encoding code interface for abort codes.
32-bit precision fixed-point numbers.

Vector

The Vector module defines a number of operations over the primitive vector type. The module is published under the named address Std and consists of a number of native functions, as well as functions defined in Move. The API for this module is as follows.

Functions

Create an empty vector. The Element type can be both a resource or copyable type.

    native public fun empty<Element>(): vector<Element>;

Create a vector of length 1 containing the passed in element.

    public fun singleton<Element>(e: Element): vector<Element>;

Destroy (deallocate) the vector v. Will abort if v is non-empty. Note: The emptiness restriction is due to the fact that Element can be a resource type, and destruction of a non-empty vector would violate resource conservation.

    native public fun destroy_empty<Element>(v: vector<Element>);

Acquire an immutable reference to the ith element of the vector v. Will abort if the index i is out of bounds for the vector v.

    native public fun borrow<Element>(v: &vector<Element>, i: u64): &Element;

Acquire a mutable reference to the ith element of the vector v. Will abort if the index i is out of bounds for the vector v.

    native public fun borrow_mut<Element>(v: &mut vector<Element>, i: u64): &mut Element;

Empty and destroy the other vector, and push each of the elements in the other vector onto the lhs vector in the same order as they occurred in other.

    public fun append<Element>(lhs: &mut vector<Element>, other: vector<Element>);

Push an element e of type Element onto the end of the vector v. May trigger a resizing of the underlying vector's memory.

    native public fun push_back<Element>(v: &mut vector<Element>, e: Element);

Pop an element from the end of the vector v in-place and return the owned value. Will abort if v is empty.

    native public fun pop_back<Element>(v: &mut vector<Element>): Element;

Remove the element at index i in the vector v and return the owned value that was previously stored at i in v. All elements occurring at indices greater than i will be shifted down by 1. Will abort if i is out of bounds for v.

    public fun remove<Element>(v: &mut vector<Element>, i: u64): Element;

Swap the ith element of the vector v with the last element and then pop this element off of the back of the vector and return the owned value that was previously stored at index i. This operation is O(1), but does not preserve ordering of elements in the vector. Aborts if the index i is out of bounds for the vector v.

    public fun swap_remove<Element>(v: &mut vector<Element>, i: u64): Element;

Swap the elements at the i'th and j'th indices in the vector v. Will abort if either of i or j are out of bounds for v.

    native public fun swap<Element>(v: &mut vector<Element>, i: u64, j: u64);

Reverse the order of the elements in the vector v in-place.

    public fun reverse<Element>(v: &mut vector<Element>);

Return the index of the first occurrence of an element in v that is equal to e. Returns (true, index) if such an element was found, and (false, 0) otherwise.

    public fun index_of<Element>(v: &vector<Element>, e: &Element): (bool, u64);

Return if an element equal to e exists in the vector v.

    public fun contains<Element>(v: &vector<Element>, e: &Element): bool;

Return the length of a vector.

    native public fun length<Element>(v: &vector<Element>): u64;

Return whether the vector v is empty.

    public fun is_empty<Element>(v: &vector<Element>): bool;

Option

The Option module defines a generic option type Option<T> that represents a value of type T that may, or may not, be present. It is published under the named address Std.

The Move option type is internally represented as a singleton vector, and may contain a value of resource or copyable kind. If you are familiar with option types in other languages, the Move Option behaves similarly to those with a couple notable exceptions since the option can contain a value of kind resource. Particularly, certain operations such as get_with_default and destroy_with_default require that the element type T be of copyable kind.

The API for the Option module is as as follows

Types

Generic type abstraction of a value that may, or may not, be present. Can contain a value of either resource or copyable kind.

    struct Option<T>;

Functions

Create an empty Option of that can contain a value of Element type.

    public fun none<Element>(): Option<Element>;

Create a non-empty Option type containing a value e of type Element.

    public fun some<Element>(e: T): Option<Element>;

Return an immutable reference to the value inside the option opt_elem Will abort if opt_elem does not contain a value.

    public fun borrow<Element>(opt_elem: &Option<Element>): &Element;

Return a reference to the value inside opt_elem if it contains one. If opt_elem does not contain a value the passed in default_ref reference will be returned. Does not abort.

    public fun borrow_with_default<Element>(opt_elem: &Option<Element>, default_ref: &Element): &Element;

Return a mutable reference to the value inside opt_elem. Will abort if opt_elem does not contain a value.

    public fun borrow_mut<Element>(opt_elem: &mut Option<Element>): &mut Element;

Convert an option value that contains a value to one that is empty in-place by removing and returning the value stored inside opt_elem. Will abort if opt_elem does not contain a value.

    public fun extract<Element>(opt_elem: &mut Option<Element>): Element;

Return the value contained inside the option opt_elem if it contains one. Will return the passed in default value if opt_elem does not contain a value. The Element type that the Option type is instantiated with must be of copyable kind in order for this function to be callable.

    public fun get_with_default<Element: copyable>(opt_elem: &Option<Element>, default: Element): Element;

Convert an empty option opt_elem to an option value that contains the value e. Will abort if opt_elem already contains a value.

    public fun fill<Element>(opt_elem: &mut Option<Element>, e: Element);

Swap the value currently contained in opt_elem with new_elem and return the previously contained value. Will abort if opt_elem does not contain a value.

    public fun swap<Element>(opt_elem: &mut Option<Element>, e: Element): Element;

Return true if opt_elem contains a value equal to the value of e_ref. Otherwise, false will be returned.

    public fun contains<Element>(opt_elem: &Option<Element>, e_ref: &Element): bool;

Return true if opt_elem does not contain a value.

    public fun is_none<Element>(opt_elem: &Option<Element>): bool;

Return true if opt_elem contains a value.

    public fun is_some<Element>(opt_elem: &Option<Element>): bool;

Unpack opt_elem and return the value that it contained. Will abort if opt_elem does not contain a value.

    public fun destroy_some<Element>(opt_elem: Option<Element>): Element;

Destroys the opt_elem value passed in. If opt_elem contained a value it will be returned otherwise, the passed in default value will be returned.

    public fun destroy_with_default<Element: copyable>(opt_elem: Option<Element>, default: Element): Element;

Destroys the opt_elem value passed in, opt_elem must be empty and not contain a value. Will abort if opt_elem contains a value.

    public fun destroy_none<Element>(opt_elem: Option<Element>);

Errors

Recall that each abort code in Move is represented as an unsigned 64-bit integer. The Errors module defines a common interface that can be used to "tag" each of these abort codes so that they can represent both the error category along with an error reason.

Error categories are declared as constants in the Errors module and are globally unique with respect to this module. Error reasons on the other hand are module-specific error codes, and can provide greater detail (perhaps, even a particular reason) about the specific error condition. This representation of a category and reason for each error code is done by dividing the abort code into two sections.

The lower 8 bits of the abort code hold the error category. The remaining 56 bits of the abort code hold the error reason. The reason should be a unique number relative to the module which raised the error and can be used to obtain more information about the error at hand. It should mostly be used for diagnostic purposes as error reasons may change over time if the module is updated.

Category	Reason
8 bits	56 bits

Since error categories are globally stable, these present the most stable API and should in general be what is used by clients to determine the messages they may present to users (whereas the reason is useful for diagnostic purposes). There are public functions in the Errors module for creating an abort code of each error category with a specific reason number (represented as a u64).

Constants

The system is in a state where the performed operation is not allowed.

    const INVALID_STATE: u8 = 1;

A specific account address was required to perform an operation, but a different address from what was expected was encounterd.

    const REQUIRES_ADDRESS: u8 = 2;

An account did not have the expected role for this operation. Useful for Role Based Access Control (RBAC) error conditions.

    const REQUIRES_ROLE: u8 = 3;

An account did not not have a required capability. Useful for RBAC error conditions.

    const REQUIRES_CAPABILITY: u8 = 4;

A resource was expected, but did not exist under an address.

    const NOT_PUBLISHED: u8 = 5;

Attempted to publish a resource under an address where one was already published.

    const ALREADY_PUBLISHED: u8 = 6;

An argument provided for an operation was invalid.

    const INVALID_ARGUMENT: u8 = 7;

A limit on a value was exceeded.

    const LIMIT_EXCEEDED: u8 = 8;

An internal error (bug) has occurred.

    const INTERNAL: u8 = 10;

A custom error category for extension points.

    const CUSTOM: u8 = 255;

Functions

Should be used in the case where invalid (global) state is encountered. Constructs an abort code with specified reason and category INVALID_STATE. Will abort if reason does not fit in 56 bits.

    public fun invalid_state(reason: u64): u64;

Should be used if an account's address does not match a specific address. Constructs an abort code with specified reason and category REQUIRES_ADDRESS. Will abort if reason does not fit in 56 bits.

    public fun requires_address(reason: u64): u64;

Should be used if a role did not match a required role when using RBAC. Constructs an abort code with specified reason and category REQUIRES_ROLE. Will abort if reason does not fit in 56 bits.

    public fun requires_role(reason: u64): u64;

Should be used if an account did not have a required capability when using RBAC. Constructs an abort code with specified reason and category REQUIRES_CAPABILITY. Should be Will abort if reason does not fit in 56 bits.

    public fun requires_capability(reason: u64): u64;

Should be used if a resource did not exist where one was expected. Constructs an abort code with specified reason and category NOT_PUBLISHED. Will abort if reason does not fit in 56 bits.

    public fun not_published(reason: u64): u64;

Should be used if a resource already existed where one was about to be published. Constructs an abort code with specified reason and category ALREADY_PUBLISHED. Will abort if reason does not fit in 56 bits.

    public fun already_published(reason: u64): u64;

Should be used if an invalid argument was passed to a function/operation. Constructs an abort code with specified reason and category INVALID_ARGUMENT. Will abort if reason does not fit in 56 bits.

    public fun invalid_argument(reason: u64): u64;

Should be used if a limit on a specific value is reached, e.g., subtracting 1 from a value of 0. Constructs an abort code with specified reason and category LIMIT_EXCEEDED. Will abort if reason does not fit in 56 bits.

    public fun limit_exceeded(reason: u64): u64;

Should be used if an internal error or bug was encountered. Constructs an abort code with specified reason and category INTERNAL. Will abort if reason does not fit in 56 bits.

    public fun internal(reason: u64): u64;

Used for extension points, should be not used under most circumstances. Constructs an abort code with specified reason and category CUSTOM. Will abort if reason does not fit in 56 bits.

    public fun custom(reason: u64): u64;

FixedPoint32

The FixedPoint32 module defines a fixed-point numeric type with 32 integer bits and 32 fractional bits. Internally, this is represented as a u64 integer wrapped in a struct to make a unique FixedPoint32 type. Since the numeric representation is a binary one, some decimal values may not be exactly representable, but it provides more than 9 decimal digits of precision both before and after the decimal point (18 digits total). For comparison, double precision floating-point has less than 16 decimal digits of precision, so you should be careful about using floating-point to convert these values to decimal.

Types

Represents a fixed-point numeric number with 32 fractional bits.

    struct FixedPoint32;

Functions

Multiply a u64 integer by a fixed-point number, truncating any fractional part of the product. This will abort if the product overflows.

    public fun multiply_u64(val: u64, multiplier: FixedPoint32): u64;

Divide a u64 integer by a fixed-point number, truncating any fractional part of the quotient. This will abort if the divisor is zero or if the quotient overflows.

    public fun divide_u64(val: u64, divisor: FixedPoint32): u64;

Create a fixed-point value from a rational number specified by its numerator and denominator. Calling this function should be preferred for using FixedPoint32::create_from_raw_value which is also available. This will abort if the denominator is zero. It will also abort if the numerator is nonzero and the ratio is not in the range $2^{-32}\ldots2^{32}-1$. When specifying decimal fractions, be careful about rounding errors: if you round to display $N$ digits after the decimal point, you can use a denominator of $10^N$ to avoid numbers where the very small imprecision in the binary representation could change the rounding, e.g., 0.0125 will round down to 0.012 instead of up to 0.013.

    public fun create_from_rational(numerator: u64, denominator: u64): FixedPoint32;

Create a fixedpoint value from a raw u64 value.

    public fun create_from_raw_value(value: u64): FixedPoint32;

Returns true if the decimal value of num is equal to zero.

    public fun is_zero(num: FixedPoint32): bool;

Accessor for the raw u64 value. Other less common operations, such as adding or subtracting FixedPoint32 values, can be done using the raw values directly.

    public fun get_raw_value(num: FixedPoint32): u64;