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    use super::TokenStreamExt;
    use core::iter;
    use proc_macro2::{Group, Ident, Literal, Punct, Span, TokenStream, TokenTree};
    use std::borrow::Cow;
    use std::rc::Rc;

    /// Types that can be interpolated inside a `quote!` invocation.
    ///
    /// [`quote!`]: macro.quote.html
    pub trait ToTokens {
        /// Write `self` to the given `TokenStream`.
        ///
        /// The token append methods provided by the [`TokenStreamExt`] extension
        /// trait may be useful for implementing `ToTokens`.
        ///
        /// [`TokenStreamExt`]: trait.TokenStreamExt.html
        ///
        /// # Example
        ///
        /// Example implementation for a struct representing Rust paths like
        /// `std::cmp::PartialEq`:
        ///
        /// ```
        /// use proc_macro2::{TokenTree, Spacing, Span, Punct, TokenStream};
        /// use quote::{TokenStreamExt, ToTokens};
        ///
        /// pub struct Path {
        ///     pub global: bool,
        ///     pub segments: Vec<PathSegment>,
        /// }
        ///
        /// impl ToTokens for Path {
        ///     fn to_tokens(&self, tokens: &mut TokenStream) {
        ///         for (i, segment) in self.segments.iter().enumerate() {
        ///             if i > 0 || self.global {
        ///                 // Double colon `::`
        ///                 tokens.append(Punct::new(':', Spacing::Joint));
        ///                 tokens.append(Punct::new(':', Spacing::Alone));
        ///             }
        ///             segment.to_tokens(tokens);
        ///         }
        ///     }
        /// }
        /// #
        /// # pub struct PathSegment;
        /// #
        /// # impl ToTokens for PathSegment {
        /// #     fn to_tokens(&self, tokens: &mut TokenStream) {
        /// #         unimplemented!()
        /// #     }
        /// # }
        /// ```
        fn to_tokens(&self, tokens: &mut TokenStream);

        /// Convert `self` directly into a `TokenStream` object.
        ///
        /// This method is implicitly implemented using `to_tokens`, and acts as a
        /// convenience method for consumers of the `ToTokens` trait.
        fn to_token_stream(&self) -> TokenStream {
            let mut tokens = TokenStream::new();
            self.to_tokens(&mut tokens);
            tokens
        }

        /// Convert `self` directly into a `TokenStream` object.
        ///
        /// This method is implicitly implemented using `to_tokens`, and acts as a
        /// convenience method for consumers of the `ToTokens` trait.
        fn into_token_stream(self) -> TokenStream
        where
            Self: Sized,
        {
            self.to_token_stream()
        }
    }

    impl<'a, T: ?Sized + ToTokens> ToTokens for &'a T {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            (**self).to_tokens(tokens);
        }
    }

    impl<'a, T: ?Sized + ToTokens> ToTokens for &'a mut T {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            (**self).to_tokens(tokens);
        }
    }

    impl<'a, T: ?Sized + ToOwned + ToTokens> ToTokens for Cow<'a, T> {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            (**self).to_tokens(tokens);
        }
    }

    impl<T: ?Sized + ToTokens> ToTokens for Box<T> {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            (**self).to_tokens(tokens);
        }
    }

    impl<T: ?Sized + ToTokens> ToTokens for Rc<T> {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            (**self).to_tokens(tokens);
        }
    }

    impl<T: ToTokens> ToTokens for Option<T> {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            if let Some(ref t) = *self {
                t.to_tokens(tokens);
            }
        }
    }

    impl ToTokens for str {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            tokens.append(Literal::string(self));
        }
    }

    impl ToTokens for String {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            self.as_str().to_tokens(tokens);
        }
    }

    macro_rules! primitive {
        ($($t:ident => $name:ident)*) => {
            $(
                impl ToTokens for $t {
                    fn to_tokens(&self, tokens: &mut TokenStream) {
                        tokens.append(Literal::$name(*self));
                    }
                }
            )*
        };
    }

    primitive! {
        i8 => i8_suffixed
        i16 => i16_suffixed
        i32 => i32_suffixed
        i64 => i64_suffixed
        i128 => i128_suffixed
        isize => isize_suffixed

        u8 => u8_suffixed
        u16 => u16_suffixed
        u32 => u32_suffixed
        u64 => u64_suffixed
        u128 => u128_suffixed
        usize => usize_suffixed

        f32 => f32_suffixed
        f64 => f64_suffixed
    }

    impl ToTokens for char {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            tokens.append(Literal::character(*self));
        }
    }

    impl ToTokens for bool {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            let word = if *self { "true" } else { "false" };
            tokens.append(Ident::new(word, Span::call_site()));
        }
    }

    impl ToTokens for Group {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            tokens.append(self.clone());
        }
    }

    impl ToTokens for Ident {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            tokens.append(self.clone());
        }
    }

    impl ToTokens for Punct {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            tokens.append(self.clone());
        }
    }

    impl ToTokens for Literal {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            tokens.append(self.clone());
        }
    }

    impl ToTokens for TokenTree {
        fn to_tokens(&self, dst: &mut TokenStream) {
            dst.append(self.clone());
        }
    }

    impl ToTokens for TokenStream {
        fn to_tokens(&self, dst: &mut TokenStream) {
            dst.extend(iter::once(self.clone()));
        }

        fn into_token_stream(self) -> TokenStream {
            self
        }
    }