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

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

Returns a copy of the value. Read more

Performs copy-assignment from source. Read more

The resulting type after dereferencing.

Dereferences the value.

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more

Immutably borrows from an owned value. Read more

Mutably borrows from an owned value. Read more

Returns the argument unchanged.

Calls U::from(self).

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

The resulting type after obtaining ownership.

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

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

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

The type returned in the event of a conversion error.

Performs the conversion.

The type returned in the event of a conversion error.

Performs the conversion.