std::mem::zeroed

fn zeroed<T>() -> T

Returns a zeroed value of any type. This function is generally unsafe to use as the zeroed bit pattern is not guaranteed to be valid for all types. It can however, be useful in cases when the value is guaranteed not to be used such as in a BoundedVec library implementing a growable vector, up to a certain length, backed by an array. The array can be initialized with zeroed values which are guaranteed to be inaccessible until the vector is pushed to. Similarly, enumerations in noir can be implemented using this method by providing zeroed values for the unused variants.

This function currently supports the following types:

• Field
• Bool
• Uint
• Array
• Slice
• String
• Tuple
• Functions

Using it on other types could result in unexpected behavior.

std::mem::checked_transmute

fn checked_transmute<T, U>(value: T) -> U

Transmutes a value of one type into the same value but with a new type U.

This function is safe to use since both types are asserted to be equal later during compilation after the concrete values for generic types become known. This function is useful for cases where the compiler may fails a type check that is expected to pass where a user knows the two types to be equal. For example, when using arithmetic generics there are cases the compiler does not see as equal, such as [Field; N*(A + B)] and [Field; N*A + N*B], which users may know to be equal. In these cases, checked_transmute can be used to cast the value to the desired type while also preserving safety by checking this equality once N, A, B are fully resolved.

Note that since this safety check is performed after type checking rather than during, no error is issued if the function containing checked_transmute is never called.

std::mem::array_refcount

fn array_refcount<T, let N: u32>(array: [T; N]) -> u32 {}

Returns the internal reference count of an array value in unconstrained code.

Arrays only have reference count in unconstrained code - using this anywhere else will return zero.

This function is mostly intended for debugging compiler optimizations but can also be used to find where array copies may be happening in unconstrained code by placing it before array mutations.

std::mem::slice_refcount

fn slice_refcount<T>(slice: [T]) -> u32 {}

Returns the internal reference count of a slice value in unconstrained code.

Slices only have reference count in unconstrained code - using this anywhere else will return zero.

This function is mostly intended for debugging compiler optimizations but can also be used to find where slice copies may be happening in unconstrained code by placing it before slice mutations.