Traits

std::default

std::default::Default

default-trait

trait Default {
    fn default() -> Self;
}

^{_{Source code: noir_stdlib/src/default.nr#L1-L5}}

Constructs a default value of a type.

Implementations:

impl Default for Field { .. }

impl Default for i8 { .. }
impl Default for i16 { .. }
impl Default for i32 { .. }
impl Default for i64 { .. }

impl Default for u8 { .. }
impl Default for u16 { .. }
impl Default for u32 { .. }
impl Default for u64 { .. }

impl Default for () { .. }
impl Default for bool { .. }

impl<T, N> Default for [T; N]
    where T: Default { .. }

impl<T> Default for [T] { .. }

impl<A, B> Default for (A, B)
    where A: Default, B: Default { .. }

impl<A, B, C> Default for (A, B, C)
    where A: Default, B: Default, C: Default { .. }

impl<A, B, C, D> Default for (A, B, C, D)
    where A: Default, B: Default, C: Default, D: Default { .. }

impl<A, B, C, D, E> Default for (A, B, C, D, E)
    where A: Default, B: Default, C: Default, D: Default, E: Default { .. }

For primitive integer types, the return value of default is 0. Container types such as arrays are filled with default values of their element type, except slices whose length is unknown and thus defaulted to zero.

std::convert

std::convert::From

from-trait

trait From<T> {
    fn from(input: T) -> Self;
}

^{_{Source code: noir_stdlib/src/convert.nr#L1-L5}}

The From trait defines how to convert from a given type T to the type on which the trait is implemented.

The Noir standard library provides a number of implementations of From between primitive types.

from-impls

// Unsigned integers

impl From<u8> for u32 { fn from(value: u8) -> u32 { value as u32 } }

impl From<u8> for u64 { fn from(value: u8) -> u64 { value as u64 } }
impl From<u32> for u64 { fn from(value: u32) -> u64 { value as u64 } }

impl From<u8> for Field { fn from(value: u8) -> Field { value as Field } }
impl From<u32> for Field { fn from(value: u32) -> Field { value as Field } }
impl From<u64> for Field { fn from(value: u64) -> Field { value as Field } }

// Signed integers

impl From<i8> for i32 { fn from(value: i8) -> i32 { value as i32 } }

impl From<i8> for i64 { fn from(value: i8) -> i64 { value as i64 } }
impl From<i32> for i64 { fn from(value: i32) -> i64 { value as i64 } }

// Booleans
impl From<bool> for u8 { fn from(value: bool) -> u8 { value as u8 } }
impl From<bool> for u32 { fn from(value: bool) -> u32 { value as u32 } }
impl From<bool> for u64 { fn from(value: bool) -> u64 { value as u64 } }
impl From<bool> for i8 { fn from(value: bool) -> i8 { value as i8 } }
impl From<bool> for i32 { fn from(value: bool) -> i32 { value as i32 } }
impl From<bool> for i64 { fn from(value: bool) -> i64 { value as i64 } }
impl From<bool> for Field { fn from(value: bool) -> Field { value as Field } }

^{_{Source code: noir_stdlib/src/convert.nr#L25-L52}}

When to implement From

As a general rule of thumb, From may be implemented in the situations where it would be suitable in Rust:

• The conversion is infallible: Noir does not provide an equivalent to Rust's TryFrom, if the conversion can fail then provide a named method instead.
• The conversion is lossless: semantically, it should not lose or discard information. For example, u32: From<u16> can losslessly convert any u16 into a valid u32 such that the original u16 can be recovered. On the other hand, u16: From<u32> should not be implemented as 2**16 is a u32 which cannot be losslessly converted into a u16.
• The conversion is value-preserving: the conceptual kind and meaning of the resulting value is the same, even though the Noir type and technical representation might be different. While it's possible to infallibly and losslessly convert a u8 into a str<2> hex representation, 4u8 and "04" are too different for str<2>: From<u8> to be implemented.
• The conversion is obvious: it's the only reasonable conversion between the two types. If there's ambiguity on how to convert between them such that the same input could potentially map to two different values then a named method should be used. For instance rather than implementing U128: From<[u8; 16]>, the methods U128::from_le_bytes and U128::from_be_bytes are used as otherwise the endianness of the array would be ambiguous, resulting in two potential values of U128 from the same byte array.

One additional recommendation specific to Noir is:

• The conversion is efficient: it's relatively cheap to convert between the two types. Due to being a ZK DSL, it's more important to avoid unnecessary computation compared to Rust. If the implementation of From would encourage users to perform unnecessary conversion, resulting in additional proving time, then it may be preferable to expose functionality such that this conversion may be avoided.

std::convert::Into

The Into trait is defined as the reciprocal of From. It should be easy to convince yourself that if we can convert to type A from type B, then it's possible to convert type B into type A.

For this reason, implementing From on a type will automatically generate a matching Into implementation. One should always prefer implementing From over Into as implementing Into will not generate a matching From implementation.

into-trait

trait Into<T> {
    fn into(self) -> T;
}

impl<T, U> Into<T> for U where T: From<U> {
  fn into(self) -> T {
      T::from(self)
  }
}

^{_{Source code: noir_stdlib/src/convert.nr#L13-L23}}

Into is most useful when passing function arguments where the types don't quite match up with what the function expects. In this case, the compiler has enough type information to perform the necessary conversion by just appending .into() onto the arguments in question.

std::cmp

std::cmp::Eq

eq-trait

trait Eq {
    fn eq(self, other: Self) -> bool;
}

^{_{Source code: noir_stdlib/src/cmp.nr#L1-L5}}

Returns true if self is equal to other. Implementing this trait on a type allows the type to be used with == and !=.

Implementations:

impl Eq for Field { .. }

impl Eq for i8 { .. }
impl Eq for i16 { .. }
impl Eq for i32 { .. }
impl Eq for i64 { .. }

impl Eq for u8 { .. }
impl Eq for u16 { .. }
impl Eq for u32 { .. }
impl Eq for u64 { .. }

impl Eq for () { .. }
impl Eq for bool { .. }

impl<T, N> Eq for [T; N]
    where T: Eq { .. }

impl<T> Eq for [T]
    where T: Eq { .. }

impl<A, B> Eq for (A, B)
    where A: Eq, B: Eq { .. }

impl<A, B, C> Eq for (A, B, C)
    where A: Eq, B: Eq, C: Eq { .. }

impl<A, B, C, D> Eq for (A, B, C, D)
    where A: Eq, B: Eq, C: Eq, D: Eq { .. }

impl<A, B, C, D, E> Eq for (A, B, C, D, E)
    where A: Eq, B: Eq, C: Eq, D: Eq, E: Eq { .. }

std::cmp::Ord

ord-trait

trait Ord {
    fn cmp(self, other: Self) -> Ordering;
}

^{_{Source code: noir_stdlib/src/cmp.nr#L102-L106}}

a.cmp(b) compares two values returning Ordering::less() if a < b, Ordering::equal() if a == b, or Ordering::greater() if a > b. Implementing this trait on a type allows <, <=, >, and >= to be used on values of the type.

std::cmp also provides max and min functions for any type which implements the Ord trait.

Implementations:

impl Ord for u8 { .. }
impl Ord for u16 { .. }
impl Ord for u32 { .. }
impl Ord for u64 { .. }

impl Ord for i8 { .. }
impl Ord for i16 { .. }
impl Ord for i32 { .. }

impl Ord for i64 { .. }

impl Ord for () { .. }
impl Ord for bool { .. }

impl<T, N> Ord for [T; N]
    where T: Ord { .. }

impl<T> Ord for [T]
    where T: Ord { .. }

impl<A, B> Ord for (A, B)
    where A: Ord, B: Ord { .. }

impl<A, B, C> Ord for (A, B, C)
    where A: Ord, B: Ord, C: Ord { .. }

impl<A, B, C, D> Ord for (A, B, C, D)
    where A: Ord, B: Ord, C: Ord, D: Ord { .. }

impl<A, B, C, D, E> Ord for (A, B, C, D, E)
    where A: Ord, B: Ord, C: Ord, D: Ord, E: Ord { .. }

std::ops

std::ops::Add, std::ops::Sub, std::ops::Mul, and std::ops::Div

These traits abstract over addition, subtraction, multiplication, and division respectively. Implementing these traits for a given type will also allow that type to be used with the corresponding operator for that trait (+ for Add, etc) in addition to the normal method names.

add-trait

trait Add {
    fn add(self, other: Self) -> Self;
}

^{_{Source code: noir_stdlib/src/ops/arith.nr#L1-L5}}

sub-trait

trait Sub {
    fn sub(self, other: Self) -> Self;
}

^{_{Source code: noir_stdlib/src/ops/arith.nr#L19-L23}}

mul-trait

trait Mul {
    fn mul(self, other: Self) -> Self;
}

^{_{Source code: noir_stdlib/src/ops/arith.nr#L37-L41}}

div-trait

trait Div {
    fn div(self, other: Self) -> Self;
}

^{_{Source code: noir_stdlib/src/ops/arith.nr#L55-L59}}

The implementations block below is given for the Add trait, but the same types that implement Add also implement Sub, Mul, and Div.

Implementations:

impl Add for Field { .. }

impl Add for i8 { .. }
impl Add for i16 { .. }
impl Add for i32 { .. }
impl Add for i64 { .. }

impl Add for u8 { .. }
impl Add for u16 { .. }
impl Add for u32 { .. }
impl Add for u64 { .. }

std::ops::Rem

rem-trait

trait Rem{
    fn rem(self, other: Self) -> Self;
}

^{_{Source code: noir_stdlib/src/ops/arith.nr#L73-L77}}

Rem::rem(a, b) is the remainder function returning the result of what is left after dividing a and b. Implementing Rem allows the % operator to be used with the implementation type.

Unlike other numeric traits, Rem is not implemented for Field.

Implementations:

impl Rem for u8 { fn rem(self, other: u8) -> u8 { self % other } }
impl Rem for u16 { fn rem(self, other: u16) -> u16 { self % other } }
impl Rem for u32 { fn rem(self, other: u32) -> u32 { self % other } }
impl Rem for u64 { fn rem(self, other: u64) -> u64 { self % other } }

impl Rem for i8 { fn rem(self, other: i8) -> i8 { self % other } }
impl Rem for i16 { fn rem(self, other: i16) -> i16 { self % other } }
impl Rem for i32 { fn rem(self, other: i32) -> i32 { self % other } }
impl Rem for i64 { fn rem(self, other: i64) -> i64 { self % other } }

std::ops::Neg

neg-trait

trait Neg {
    fn neg(self) -> Self;
}

^{_{Source code: noir_stdlib/src/ops/arith.nr#L89-L93}}

Neg::neg is equivalent to the unary negation operator -.

Implementations:

neg-trait-impls

impl Neg for Field { fn neg(self) -> Field { -self } }

impl Neg for i8 { fn neg(self) -> i8 { -self } }
impl Neg for i16 { fn neg(self) -> i16 { -self } }
impl Neg for i32 { fn neg(self) -> i32 { -self } }
impl Neg for i64 { fn neg(self) -> i64 { -self } }

^{_{Source code: noir_stdlib/src/ops/arith.nr#L95-L102}}

std::ops::Not

not-trait

trait Not {
    fn not(self: Self) -> Self;
}

^{_{Source code: noir_stdlib/src/ops/bit.nr#L1-L5}}

Not::not is equivalent to the unary bitwise NOT operator !.

Implementations:

not-trait-impls

impl Not for bool { fn not(self) -> bool { !self } }

impl Not for u64 { fn not(self) -> u64 { !self } }
impl Not for u32 { fn not(self) -> u32 { !self } }
impl Not for u16 { fn not(self) -> u16 { !self } }
impl Not for u8 { fn not(self) -> u8 { !self } }
impl Not for u1 { fn not(self) -> u1 { !self } }

impl Not for i8 { fn not(self) -> i8 { !self } }
impl Not for i16 { fn not(self) -> i16 { !self } }
impl Not for i32 { fn not(self) -> i32 { !self } }
impl Not for i64 { fn not(self) -> i64 { !self } }

^{_{Source code: noir_stdlib/src/ops/bit.nr#L7-L20}}

std::ops::{ BitOr, BitAnd, BitXor }

bitor-trait

trait BitOr {
    fn bitor(self, other: Self) -> Self;
}

^{_{Source code: noir_stdlib/src/ops/bit.nr#L22-L26}}

bitand-trait

trait BitAnd {
    fn bitand(self, other: Self) -> Self;
}

^{_{Source code: noir_stdlib/src/ops/bit.nr#L40-L44}}

bitxor-trait

trait BitXor {
    fn bitxor(self, other: Self) -> Self;
}

^{_{Source code: noir_stdlib/src/ops/bit.nr#L58-L62}}

Traits for the bitwise operations |, &, and ^.

Implementing BitOr, BitAnd or BitXor for a type allows the |, &, or ^ operator respectively to be used with the type.

The implementations block below is given for the BitOr trait, but the same types that implement BitOr also implement BitAnd and BitXor.

Implementations:

impl BitOr for bool { fn bitor(self, other: bool) -> bool { self | other } }

impl BitOr for u8 { fn bitor(self, other: u8) -> u8 { self | other } }
impl BitOr for u16 { fn bitor(self, other: u16) -> u16 { self | other } }
impl BitOr for u32 { fn bitor(self, other: u32) -> u32 { self | other } }
impl BitOr for u64 { fn bitor(self, other: u64) -> u64 { self | other } }

impl BitOr for i8 { fn bitor(self, other: i8) -> i8 { self | other } }
impl BitOr for i16 { fn bitor(self, other: i16) -> i16 { self | other } }
impl BitOr for i32 { fn bitor(self, other: i32) -> i32 { self | other } }
impl BitOr for i64 { fn bitor(self, other: i64) -> i64 { self | other } }

std::ops::{ Shl, Shr }

shl-trait

trait Shl {
    fn shl(self, other: u8) -> Self;
}

^{_{Source code: noir_stdlib/src/ops/bit.nr#L76-L80}}

shr-trait

trait Shr {
    fn shr(self, other: u8) -> Self;
}

^{_{Source code: noir_stdlib/src/ops/bit.nr#L93-L97}}

Traits for a bit shift left and bit shift right.

Implementing Shl for a type allows the left shift operator (<<) to be used with the implementation type. Similarly, implementing Shr allows the right shift operator (>>) to be used with the type.

Note that bit shifting is not currently implemented for signed types.

The implementations block below is given for the Shl trait, but the same types that implement Shl also implement Shr.

Implementations:

impl Shl for u8 { fn shl(self, other: u8) -> u8 { self << other } }
impl Shl for u16 { fn shl(self, other: u16) -> u16 { self << other } }
impl Shl for u32 { fn shl(self, other: u32) -> u32 { self << other } }
impl Shl for u64 { fn shl(self, other: u64) -> u64 { self << other } }