Trait wasmtime_environ::__core::prelude::rust_2024::Default

1.0.0 · source ·
pub trait Default: Sized {
    // Required method
    fn default() -> Self;
}
Expand description

A trait for giving a type a useful default value.

Sometimes, you want to fall back to some kind of default value, and don’t particularly care what it is. This comes up often with structs that define a set of options:

struct SomeOptions {
    foo: i32,
    bar: f32,
}

How can we define some default values? You can use Default:

#[derive(Default)]
struct SomeOptions {
    foo: i32,
    bar: f32,
}

fn main() {
    let options: SomeOptions = Default::default();
}

Now, you get all of the default values. Rust implements Default for various primitives types.

If you want to override a particular option, but still retain the other defaults:

fn main() {
    let options = SomeOptions { foo: 42, ..Default::default() };
}

§Derivable

This trait can be used with #[derive] if all of the type’s fields implement Default. When derived, it will use the default value for each field’s type.

§enums

When using #[derive(Default)] on an enum, you need to choose which unit variant will be default. You do this by placing the #[default] attribute on the variant.

#[derive(Default)]
enum Kind {
    #[default]
    A,
    B,
    C,
}

You cannot use the #[default] attribute on non-unit or non-exhaustive variants.

The #[default] attribute was stabilized in Rust 1.62.0.

§How can I implement Default?

Provide an implementation for the default() method that returns the value of your type that should be the default:

enum Kind {
    A,
    B,
    C,
}

impl Default for Kind {
    fn default() -> Self { Kind::A }
}

§Examples

#[derive(Default)]
struct SomeOptions {
    foo: i32,
    bar: f32,
}

Required Methods§

1.0.0 · source

fn default() -> Self

Returns the “default value” for a type.

Default values are often some kind of initial value, identity value, or anything else that may make sense as a default.

§Examples

Using built-in default values:

let i: i8 = Default::default();
let (x, y): (Option<String>, f64) = Default::default();
let (a, b, (c, d)): (i32, u32, (bool, bool)) = Default::default();

Making your own:

enum Kind {
    A,
    B,
    C,
}

impl Default for Kind {
    fn default() -> Self { Kind::A }
}

Object Safety§

This trait is not object safe.

Implementors§

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impl Default for &str

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impl Default for &CStr

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impl Default for &OsStr

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impl Default for &mut str

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impl Default for PrefilterConfig

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impl Default for MemoryInitialization

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impl Default for TableInitialization

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impl Default for AsciiChar

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impl Default for bool

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impl Default for char

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impl Default for f16

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impl Default for f32

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impl Default for f64

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impl Default for f128

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impl Default for i8

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impl Default for i16

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impl Default for i32

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impl Default for i64

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impl Default for i128

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impl Default for isize

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impl Default for u8

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impl Default for u16

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impl Default for u32

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impl Default for u64

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impl Default for u128

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impl Default for ()

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impl Default for usize

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impl Default for anyhow::Chain<'_>

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impl Default for Config

The defaults are that of https://url.spec.whatwg.org/#idna

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impl Default for Errors

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impl Default for Idna

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impl Default for FinderBuilder

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impl Default for IgnoredAny

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impl Default for DefaultToHost

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impl Default for DefaultToUnknown

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impl Default for AddressMapSection

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impl Default for FilePos

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impl Default for Module

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impl Default for ModuleTypes

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impl Default for ModuleTypesBuilder

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impl Default for TrapEncodingBuilder

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impl Default for Tunables

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impl Default for WasmFileInfo

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impl Default for WasmFunctionInfo

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impl Default for FuncValidatorAllocations

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impl Default for Parser

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impl Default for Validator

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impl Default for WasmFeatures

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impl Default for Error

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impl Default for SipHasher

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impl Default for PhantomPinned

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impl Default for Alignment

Returns Alignment::MIN, which is valid for any type.

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impl Default for RangeFull

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impl Default for AtomicBool

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impl Default for AtomicI8

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impl Default for AtomicI16

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impl Default for AtomicI32

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impl Default for AtomicI64

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impl Default for AtomicIsize

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impl Default for AtomicU8

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impl Default for AtomicU16

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impl Default for AtomicU32

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impl Default for AtomicU64

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impl Default for AtomicUsize

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impl Default for Duration

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impl Default for Global

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impl Default for Box<str>

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impl Default for Box<CStr>

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impl Default for Box<OsStr>

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impl Default for CString

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impl Default for Rc<str>

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impl Default for Rc<CStr>

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impl Default for String

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impl Default for Arc<str>

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impl Default for Arc<CStr>

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impl Default for System

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impl Default for OsString

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impl Default for FileTimes

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impl Default for DefaultHasher

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impl Default for RandomState

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impl Default for std::io::util::Empty

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impl Default for Sink

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impl Default for PathBuf

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impl Default for ExitCode

The default value is ExitCode::SUCCESS

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impl Default for ExitStatus

The default value is one which indicates successful completion.

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impl Default for Condvar

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impl Default for Abbreviations

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impl Default for AbbreviationsCache

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impl Default for Augmentation

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impl Default for BaseAddresses

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impl Default for BigEndian

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impl Default for BigEndian

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impl Default for DebugInfoOffsets

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impl Default for Dwarf

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impl Default for DwarfFileType

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impl Default for Endianness

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impl Default for Expression

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impl Default for FileInfo

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impl Default for FrameTable

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impl Default for Hasher

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impl Default for ImageSectionHeader

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impl Default for LineEncoding

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impl Default for LineStringTable

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impl Default for LittleEndian

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impl Default for LittleEndian

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impl Default for LocationListTable

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impl Default for Pointer

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impl Default for RangeListTable

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impl Default for Relocation

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impl Default for RunTimeEndian

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impl Default for SectionBaseAddresses

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impl Default for SectionIndex

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impl Default for SectionRange

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impl Default for StringTable

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impl Default for SymbolIndex

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impl Default for UnitTable

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impl Default for VersionIndex

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impl<'a> Default for MetadataBuilder<'a>

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impl<'a> Default for RecordBuilder<'a>

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impl<'a> Default for DebugInfoData<'a>

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impl<'a> Default for NameSection<'a>

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impl<'a, K, V> Default for alloc::collections::btree::map::Iter<'a, K, V>
where K: 'a, V: 'a,

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impl<'a, K, V> Default for alloc::collections::btree::map::IterMut<'a, K, V>
where K: 'a, V: 'a,

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impl<'data> Default for ModuleTranslation<'data>

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impl<'data> Default for Bytes<'data>

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impl<'data> Default for ObjectMap<'data>

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impl<'data> Default for ObjectMapEntry<'data>

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impl<'data> Default for RelocationBlockIterator<'data>

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impl<'data> Default for SectionTable<'data>

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impl<'data> Default for Version<'data>

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impl<'data, E> Default for LoadCommandIterator<'data, E>
where E: Default + Endian,

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impl<'data, Elf> Default for VersionTable<'data, Elf>
where Elf: FileHeader,

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impl<'data, Elf, R> Default for SectionTable<'data, Elf, R>
where Elf: Default + FileHeader, R: Default + ReadRef<'data>, <Elf as FileHeader>::SectionHeader: Default,

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impl<'data, Elf, R> Default for SymbolTable<'data, Elf, R>
where Elf: FileHeader, R: ReadRef<'data>,

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impl<'data, Mach, R> Default for SymbolTable<'data, Mach, R>
where Mach: MachHeader, R: ReadRef<'data>,

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impl<'data, R> Default for StringTable<'data, R>
where R: ReadRef<'data>,

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impl<'data, R> Default for SymbolTable<'data, R>
where R: ReadRef<'data>,

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impl<'input, Endian> Default for EndianSlice<'input, Endian>
where Endian: Default + Endianity,

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impl<'s, T> Default for SliceVec<'s, T>

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impl<A> Default for TinyVec<A>
where A: Array,

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impl<A> Default for ArrayVec<A>
where A: Array,

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impl<A, B> Default for wasmtime_environ::__core::iter::Chain<A, B>
where A: Default, B: Default,

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impl<B> Default for Cow<'_, B>
where B: ToOwned + ?Sized, <B as ToOwned>::Owned: Default,

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impl<E> Default for CompressionHeader32<E>
where E: Default + Endian,

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impl<E> Default for CompressionHeader64<E>
where E: Default + Endian,

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impl<E> Default for I16<E>
where E: Default + Endian,

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impl<E> Default for I16Bytes<E>
where E: Default + Endian,

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impl<E> Default for I32<E>
where E: Default + Endian,

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impl<E> Default for I32Bytes<E>
where E: Default + Endian,

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impl<E> Default for I64<E>
where E: Default + Endian,

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impl<E> Default for I64Bytes<E>
where E: Default + Endian,

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impl<E> Default for Sym32<E>
where E: Default + Endian,

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impl<E> Default for Sym64<E>
where E: Default + Endian,

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impl<E> Default for U16<E>
where E: Default + Endian,

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impl<E> Default for U16Bytes<E>
where E: Default + Endian,

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impl<E> Default for U32<E>
where E: Default + Endian,

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impl<E> Default for U32Bytes<E>
where E: Default + Endian,

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impl<E> Default for U64<E>
where E: Default + Endian,

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impl<E> Default for U64Bytes<E>
where E: Default + Endian,

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impl<H> Default for BuildHasherDefault<H>

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impl<I> Default for Cloned<I>
where I: Default,

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impl<I> Default for Copied<I>
where I: Default,

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impl<I> Default for Enumerate<I>
where I: Default,

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impl<I> Default for Flatten<I>
where I: Default + Iterator, <I as Iterator>::Item: IntoIterator,

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impl<I> Default for Fuse<I>
where I: Default,

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impl<I> Default for Rev<I>
where I: Default,

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impl<Idx> Default for wasmtime_environ::__core::range::legacy::Range<Idx>
where Idx: Default,

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impl<Idx> Default for wasmtime_environ::__core::range::Range<Idx>
where Idx: Default,

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impl<K> Default for EntitySet<K>
where K: EntityRef,

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impl<K, V> Default for PrimaryMap<K, V>
where K: EntityRef,

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impl<K, V> Default for SecondaryMap<K, V>
where K: EntityRef, V: Clone + Default,

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impl<K, V> Default for BTreeMap<K, V>

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impl<K, V> Default for Keys<'_, K, V>

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impl<K, V> Default for alloc::collections::btree::map::Range<'_, K, V>

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impl<K, V> Default for Values<'_, K, V>

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impl<K, V, A> Default for alloc::collections::btree::map::IntoIter<K, V, A>
where A: Allocator + Default + Clone,

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impl<K, V, A> Default for IntoKeys<K, V, A>
where A: Allocator + Default + Clone,

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impl<K, V, A> Default for IntoValues<K, V, A>
where A: Allocator + Default + Clone,

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impl<K, V, S> Default for std::collections::hash::map::HashMap<K, V, S>
where S: Default,

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impl<K, V, S> Default for IndexMap<K, V, S>
where S: Default,

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impl<K, V, S, A> Default for hashbrown::map::HashMap<K, V, S, A>
where S: Default, A: Default + Allocator + Clone,

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impl<R> Default for CfaRule<R>
where R: Reader,

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impl<R> Default for DebugAbbrev<R>
where R: Default,

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impl<R> Default for DebugAddr<R>
where R: Default,

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impl<R> Default for DebugAranges<R>
where R: Default,

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impl<R> Default for DebugCuIndex<R>
where R: Default,

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impl<R> Default for DebugInfo<R>
where R: Default,

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impl<R> Default for DebugLine<R>
where R: Default,

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impl<R> Default for DebugLineStr<R>
where R: Default,

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impl<R> Default for DebugLoc<R>
where R: Default,

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impl<R> Default for DebugLocLists<R>
where R: Default,

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impl<R> Default for DebugRanges<R>
where R: Default,

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impl<R> Default for DebugRngLists<R>
where R: Default,

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impl<R> Default for DebugStr<R>
where R: Default,

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impl<R> Default for DebugStrOffsets<R>
where R: Default,

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impl<R> Default for DebugTuIndex<R>
where R: Default,

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impl<R> Default for DebugTypes<R>
where R: Default,

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impl<R> Default for Dwarf<R>
where R: Default,

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impl<R> Default for LocationLists<R>
where R: Default,

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impl<R> Default for RangeIter<R>
where R: Reader,

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impl<R> Default for RangeLists<R>
where R: Default,

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impl<R, A> Default for UnwindContext<R, A>
where R: Reader, A: UnwindContextStorage<R>,

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impl<R, S> Default for UnwindTableRow<R, S>
where R: Reader, S: UnwindContextStorage<R>,

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impl<T> Default for &[T]

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impl<T> Default for &mut [T]

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impl<T> Default for Option<T>

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impl<T> Default for [T; 0]

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impl<T> Default for [T; 1]
where T: Default,

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impl<T> Default for [T; 2]
where T: Default,

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impl<T> Default for [T; 3]
where T: Default,

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impl<T> Default for [T; 4]
where T: Default,

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impl<T> Default for [T; 5]
where T: Default,

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impl<T> Default for [T; 6]
where T: Default,

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impl<T> Default for [T; 7]
where T: Default,

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impl<T> Default for [T; 8]
where T: Default,

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impl<T> Default for [T; 9]
where T: Default,

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impl<T> Default for [T; 10]
where T: Default,

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impl<T> Default for [T; 11]
where T: Default,

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impl<T> Default for [T; 12]
where T: Default,

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impl<T> Default for [T; 13]
where T: Default,

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impl<T> Default for [T; 14]
where T: Default,

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impl<T> Default for [T; 15]
where T: Default,

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impl<T> Default for [T; 16]
where T: Default,

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impl<T> Default for [T; 17]
where T: Default,

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impl<T> Default for [T; 18]
where T: Default,

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impl<T> Default for [T; 19]
where T: Default,

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impl<T> Default for [T; 20]
where T: Default,

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impl<T> Default for [T; 21]
where T: Default,

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impl<T> Default for [T; 22]
where T: Default,

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impl<T> Default for [T; 23]
where T: Default,

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impl<T> Default for [T; 24]
where T: Default,

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impl<T> Default for [T; 25]
where T: Default,

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impl<T> Default for [T; 26]
where T: Default,

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impl<T> Default for [T; 27]
where T: Default,

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impl<T> Default for [T; 28]
where T: Default,

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impl<T> Default for [T; 29]
where T: Default,

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impl<T> Default for [T; 30]
where T: Default,

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impl<T> Default for [T; 31]
where T: Default,

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impl<T> Default for [T; 32]
where T: Default,

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impl<T> Default for (T₁, T₂, …, Tₙ)
where T: Default,

This trait is implemented for tuples up to twelve items long.

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impl<T> Default for PackedOption<T>
where T: ReservedValue,

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impl<T> Default for EntityList<T>

Create an empty list.

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impl<T> Default for ListPool<T>

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impl<T> Default for Cell<T>
where T: Default,

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impl<T> Default for LazyCell<T>
where T: Default,

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impl<T> Default for OnceCell<T>

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impl<T> Default for RefCell<T>
where T: Default,

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impl<T> Default for SyncUnsafeCell<T>
where T: Default,

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impl<T> Default for UnsafeCell<T>
where T: Default,

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impl<T> Default for Reverse<T>
where T: Default,

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impl<T> Default for wasmtime_environ::__core::iter::Empty<T>

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impl<T> Default for PhantomData<T>
where T: ?Sized,

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impl<T> Default for ManuallyDrop<T>
where T: Default + ?Sized,

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impl<T> Default for Saturating<T>
where T: Default,

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impl<T> Default for Wrapping<T>
where T: Default,

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impl<T> Default for AssertUnwindSafe<T>
where T: Default,

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impl<T> Default for wasmtime_environ::__core::slice::Iter<'_, T>

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impl<T> Default for wasmtime_environ::__core::slice::IterMut<'_, T>

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impl<T> Default for AtomicPtr<T>

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impl<T> Default for Exclusive<T>
where T: Default + ?Sized,

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impl<T> Default for Box<[T]>

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impl<T> Default for Box<T>
where T: Default,

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impl<T> Default for BinaryHeap<T>
where T: Ord,

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impl<T> Default for alloc::collections::binary_heap::IntoIter<T>

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impl<T> Default for BTreeSet<T>

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impl<T> Default for alloc::collections::btree::set::Iter<'_, T>

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impl<T> Default for alloc::collections::btree::set::Range<'_, T>

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impl<T> Default for alloc::collections::linked_list::IntoIter<T>

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impl<T> Default for alloc::collections::linked_list::Iter<'_, T>

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impl<T> Default for alloc::collections::linked_list::IterMut<'_, T>

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impl<T> Default for LinkedList<T>

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impl<T> Default for VecDeque<T>

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impl<T> Default for Rc<[T]>

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impl<T> Default for Rc<T>
where T: Default,

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impl<T> Default for alloc::rc::Weak<T>

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impl<T> Default for Arc<[T]>

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impl<T> Default for Arc<T>
where T: Default,

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impl<T> Default for alloc::sync::Weak<T>

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impl<T> Default for Vec<T>

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impl<T> Default for Cursor<T>
where T: Default,

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impl<T> Default for LazyLock<T>
where T: Default,

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impl<T> Default for Mutex<T>
where T: Default + ?Sized,

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impl<T> Default for OnceLock<T>

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impl<T> Default for ReentrantLock<T>
where T: Default,

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impl<T> Default for RwLock<T>
where T: Default,

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impl<T> Default for SymbolMap<T>
where T: Default + SymbolMapEntry,

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impl<T, A> Default for RawTable<T, A>
where A: Allocator + Clone + Default,

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impl<T, A> Default for alloc::collections::btree::set::IntoIter<T, A>
where A: Allocator + Default + Clone,

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impl<T, A> Default for alloc::vec::into_iter::IntoIter<T, A>
where A: Allocator + Default,

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impl<T, S> Default for std::collections::hash::set::HashSet<T, S>
where S: Default,

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impl<T, S> Default for IndexSet<T, S>
where S: Default,

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impl<T, S, A> Default for hashbrown::set::HashSet<T, S, A>
where S: Default, A: Default + Allocator + Clone,

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impl<T, const N: usize> Default for Mask<T, N>

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impl<T, const N: usize> Default for Simd<T, N>

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impl<W> Default for DebugAbbrev<W>
where W: Default + Writer,

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impl<W> Default for DebugFrame<W>
where W: Default + Writer,

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impl<W> Default for DebugInfo<W>
where W: Default + Writer,

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impl<W> Default for DebugLine<W>
where W: Default + Writer,

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impl<W> Default for DebugLineStr<W>
where W: Default + Writer,

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impl<W> Default for DebugLoc<W>
where W: Default + Writer,

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impl<W> Default for DebugLocLists<W>
where W: Default + Writer,

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impl<W> Default for DebugRanges<W>
where W: Default + Writer,

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impl<W> Default for DebugRngLists<W>
where W: Default + Writer,

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impl<W> Default for DebugStr<W>
where W: Default + Writer,

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impl<W> Default for EhFrame<W>
where W: Default + Writer,

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impl<W> Default for Sections<W>
where W: Default + Writer,