# Struct syn::parse::StepCursor

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    pub struct StepCursor<'c, 'a> { /* private fields */ }

Expand description

Cursor state associated with speculative parsing.

This type is the input of the closure provided to `ParseStream::step`.

## Example

    use proc_macro2::TokenTree;
    use syn::Result;
    use syn::parse::ParseStream;

    // This function advances the stream past the next occurrence of `@`. If
    // no `@` is present in the stream, the stream position is unchanged and
    // an error is returned.
    fn skip_past_next_at(input: ParseStream) -> Result<()> {
        input.step(|cursor| {
            let mut rest = *cursor;
            while let Some((tt, next)) = rest.token_tree() {
                match &tt {
                    TokenTree::Punct(punct) if punct.as_char() == '@' => {
                        return Ok(((), next));
                    }
                    _ => rest = next,
                }
            }
            Err(cursor.error("no `@` was found after this point"))
        })
    }

## Implementations

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### impl<'c, 'a> StepCursor<'c, 'a>

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#### pub fn error<T: Display>(self, message: T) -> Error

Triggers an error at the current position of the parse stream.

The `ParseStream::step` invocation will return this same error without advancing the stream state.

## Trait Implementations

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### impl<'c, 'a> Clone for StepCursor<'c, 'a>

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

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<'c, 'a> Deref for StepCursor<'c, 'a>

#### type Target = Cursor<'c>

The resulting type after dereferencing.

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#### fn deref(&self) -> &Self::Target

Dereferences the value.

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### impl<'c, 'a> Copy for StepCursor<'c, 'a>

## Auto Trait Implementations

### impl<'c, 'a> RefUnwindSafe for StepCursor<'c, 'a>

### impl<'c, 'a> !Send for StepCursor<'c, 'a>

### impl<'c, 'a> !Sync for StepCursor<'c, 'a>

### impl<'c, 'a> Unpin for StepCursor<'c, 'a>

### impl<'c, 'a> UnwindSafe for StepCursor<'c, 'a>

## 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, 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.