# MatchesError in clap::parser - Rust
Violation of [`ArgMatches`][crate::ArgMatches] assumptions
Keywords: rust, rustlang, rust-lang, MatchesError

# Enum clap::parser::MatchesError

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    #[non_exhaustive]
    pub enum MatchesError {
        Downcast {
            actual: AnyValueId,
            expected: AnyValueId,
        },
        UnknownArgument {},
    }

Expand description

Violation of `ArgMatches` assumptions

## Variants (Non-exhaustive)

This enum is marked as non-exhaustive
Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

### `Downcast`

#### Fields

This variant is marked as non-exhaustive
Non-exhaustive enum variants could have additional fields added in future. Therefore, non-exhaustive enum variants cannot be constructed in external crates and cannot be matched against.
`actual: AnyValueId`

Type for value stored in `ArgMatches`

`expected: AnyValueId`

The target type to downcast to

Failed to downcast `AnyValue` to the specified type

### `UnknownArgument`

#### Fields

This variant is marked as non-exhaustive
Non-exhaustive enum variants could have additional fields added in future. Therefore, non-exhaustive enum variants cannot be constructed in external crates and cannot be matched against.

Argument not defined in `Command`

## Trait Implementations

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### impl Clone for MatchesError

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#### fn clone(&self) -> MatchesError

Returns a copy of the value. Read more

1.0.0 · source

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

Performs copy-assignment from `source`. Read more

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### impl Debug for MatchesError

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

Formats the value using the given formatter. Read more

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### impl Display for MatchesError

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

Formats the value using the given formatter. Read more

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### impl Error for MatchesError

1.30.0 · source

#### fn source(&self) -> Option<&(dyn Error + 'static)>

The lower-level source of this error, if any. Read more

1.0.0 · source

#### fn description(&self) -> &str

👎 Deprecated since 1.42.0:

use the Display impl or to_string()

Read more
1.0.0 · source

#### fn cause(&self) -> Option<&dyn Error>

👎 Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

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#### fn provide(&'a self, req: &mut Demand<'a>)

🔬 This is a nightly-only experimental API. (`error_generic_member_access`)

Provides type based access to context intended for error reports. Read more

## Auto Trait Implementations

### impl RefUnwindSafe for MatchesError

### impl Send for MatchesError

### impl Sync for MatchesError

### impl Unpin for MatchesError

### impl UnwindSafe for MatchesError

## Blanket Implementations

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### impl<T> Any for T where
T: 'static + ?Sized,

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#### fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more

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### impl<T> Borrow<T> for T where
T: ?Sized,

const: unstable · source

#### fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more

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### impl<T> BorrowMut<T> for T where
T: ?Sized,

const: unstable · source

#### fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more

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### impl<T> From<T> for T

const: unstable · source

#### fn from(t: T) -> T

Returns the argument unchanged.

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### impl<T, U> Into<U> for T where
U: From<T>,

const: unstable · source

#### fn into(self) -> U

Calls `U::from(self)`.

That is, this conversion is whatever the implementation of `From<T> for U` chooses to do.

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### impl<T> ToOwned for T where
T: Clone,

#### type Owned = T

The resulting type after obtaining ownership.

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#### fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more

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#### fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more

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### impl<T> ToString for T where
T: Display + ?Sized,

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#### default fn to_string(&self) -> String

Converts the given value to a `String`. Read more

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### impl<T, U> TryFrom<U> for T where
U: Into<T>,

#### type Error = Infallible

The type returned in the event of a conversion error.

const: unstable · source

#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.

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### impl<T, U> TryInto<U> for T where
U: TryFrom<T>,

#### type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.

const: unstable · source

#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.