Enum wasmtime::component::Val

pub enum Val {
    Bool(bool),
    S8(i8),
    U8(u8),
    S16(i16),
    U16(u16),
    S32(i32),
    U32(u32),
    S64(i64),
    U64(u64),
    Float32(f32),
    Float64(f64),
    Char(char),
    String(String),
    List(Vec<Val>),
    Record(Vec<(String, Val)>),
    Tuple(Vec<Val>),
    Variant(String, Option<Box<Val>>),
    Enum(String),
    Option(Option<Box<Val>>),
    Result(Result<Option<Box<Val>>, Option<Box<Val>>>),
    Flags(Vec<String>),
    Resource(ResourceAny),
}

Available on crate features runtime and component-model only.

Represents possible runtime values which a component function can either consume or produce

This is a dynamic representation of possible values in the component model. Note that this is not an efficient representation but is instead intended to be a flexible and somewhat convenient representation. The most efficient representation of component model types is to use the bindgen! macro to generate native Rust types with specialized liftings and lowerings.

This type is used in conjunction with Func::call for example if the signature of a component is not statically known ahead of time.

Equality and Val

This type implements both the Rust PartialEq and Eq traits. This type additionally contains values which are not necessarily easily equated, however, such as floats (Float32 and Float64) and resources. Equality does require that two values have the same type, and then these cases are handled as:

• Floats are tested if they are “semantically the same” meaning all NaN values are equal to all other NaN values. Additionally zero values must be exactly the same, so positive zero is not equal to negative zero. The primary use case at this time is fuzzing-related equality which this is sufficient for.

• Resources are tested if their types and indices into the host table are equal. This does not compare the underlying representation so borrows of the same guest resource are not considered equal. This additionally doesn’t go further and test for equality in the guest itself (for example two different heap allocations of Box<u32> can be equal in normal Rust if they contain the same value, but will never be considered equal when compared as Val::Resources).

In general if a strict guarantee about equality is required here it’s recommended to “build your own” as this equality intended for fuzzing Wasmtime may not be suitable for you.

Component model types and Val

The Val type here does not contain enough information to say what the component model type of a Val is. This is instead more of an AST of sorts. For example the Val::Enum only carries information about a single discriminant, not the entire enumeration or what it’s a discriminant of.

This means that when a Val is passed to Wasmtime, for example as a function parameter when calling a function or as a return value from an host-defined imported function, then it must pass a type-check. Instances of Val are type-checked against what’s required by the component itself.

Variants

Bool(bool)

S8(i8)

U8(u8)

S16(i16)

U16(u16)

S32(i32)

U32(u32)

S64(i64)

U64(u64)

Float32(f32)

Float64(f64)

Char(char)

String(String)

List(Vec<Val>)

Record(Vec<(String, Val)>)

Tuple(Vec<Val>)

Variant(String, Option<Box<Val>>)

Enum(String)

Option(Option<Box<Val>>)

Result(Result<Option<Box<Val>>, Option<Box<Val>>>)

Flags(Vec<String>)

Resource(ResourceAny)

Trait Implementations

impl Clone for Val

fn clone(&self) -> Val

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Val

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl PartialEq for Val

fn eq(&self, other: &Self) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Eq for Val