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    use alloc::{rc::Rc, vec::Vec};
    use core::cell::RefCell;
    use core::fmt;
    use core::u32;
    use func::FuncRef;
    use module::check_limits;
    use parity_wasm::elements::ResizableLimits;
    use Error;

    /// Reference to a table (See [`TableInstance`] for details).
    ///
    /// This reference has a reference-counting semantics.
    ///
    /// [`TableInstance`]: struct.TableInstance.html
    ///
    #[derive(Clone, Debug)]
    pub struct TableRef(Rc<TableInstance>);

    impl ::core::ops::Deref for TableRef {
        type Target = TableInstance;
        fn deref(&self) -> &TableInstance {
            &self.0
        }
    }

    /// Runtime representation of a table.
    ///
    /// A table is a array of untyped functions. It allows wasm code to call functions
    /// indirectly through a dynamic index into a table. For example, this allows emulating function
    /// pointers by way of table indices.
    ///
    /// Table is created with an initial size but can be grown dynamically via [`grow`] method.
    /// Growth can be limited by an optional maximum size.
    ///
    /// In future, a table might be extended to be able to hold not only functions but different types.
    ///
    /// [`grow`]: #method.grow
    ///
    pub struct TableInstance {
        /// Table limits.
        limits: ResizableLimits,
        /// Table memory buffer.
        buffer: RefCell<Vec<Option<FuncRef>>>,
    }

    impl fmt::Debug for TableInstance {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            f.debug_struct("TableInstance")
                .field("limits", &self.limits)
                .field("buffer.len", &self.buffer.borrow().len())
                .finish()
        }
    }

    impl TableInstance {
        /// Allocate a table instance.
        ///
        /// The table allocated with initial size, specified by `initial_size`.
        /// Maximum size can be specified by `maximum_size`.
        ///
        /// All table elements are allocated uninitialized.
        ///
        /// # Errors
        ///
        /// Returns `Err` if `initial_size` is greater than `maximum_size`.
        pub fn alloc(initial_size: u32, maximum_size: Option<u32>) -> Result<TableRef, Error> {
            let table = TableInstance::new(ResizableLimits::new(initial_size, maximum_size))?;
            Ok(TableRef(Rc::new(table)))
        }

        fn new(limits: ResizableLimits) -> Result<TableInstance, Error> {
            check_limits(&limits)?;
            Ok(TableInstance {
                buffer: RefCell::new(vec![None; limits.initial() as usize]),
                limits: limits,
            })
        }

        /// Return table limits.
        pub(crate) fn limits(&self) -> &ResizableLimits {
            &self.limits
        }

        /// Returns size this table was created with.
        pub fn initial_size(&self) -> u32 {
            self.limits.initial()
        }

        /// Returns maximum size `TableInstance` can grow to.
        pub fn maximum_size(&self) -> Option<u32> {
            self.limits.maximum()
        }

        /// Returns current size of the table.
        pub fn current_size(&self) -> u32 {
            self.buffer.borrow().len() as u32
        }

        /// Increases the size of the table by given number of elements.
        ///
        /// # Errors
        ///
        /// Returns `Err` if tried to allocate more elements than permited by limit.
        pub fn grow(&self, by: u32) -> Result<(), Error> {
            let mut buffer = self.buffer.borrow_mut();
            let maximum_size = self.maximum_size().unwrap_or(u32::MAX);
            let new_size = self
                .current_size()
                .checked_add(by)
                .and_then(|new_size| {
                    if maximum_size < new_size {
                        None
                    } else {
                        Some(new_size)
                    }
                })
                .ok_or_else(|| {
                    Error::Table(format!(
                        "Trying to grow table by {} items when there are already {} items",
                        by,
                        self.current_size(),
                    ))
                })?;
            buffer.resize(new_size as usize, None);
            Ok(())
        }

        /// Get the specific value in the table
        pub fn get(&self, offset: u32) -> Result<Option<FuncRef>, Error> {
            let buffer = self.buffer.borrow();
            let buffer_len = buffer.len();
            let table_elem = buffer.get(offset as usize).cloned().ok_or_else(|| {
                Error::Table(format!(
                    "trying to read table item with index {} when there are only {} items",
                    offset, buffer_len
                ))
            })?;
            Ok(table_elem)
        }

        /// Set the table element to the specified function.
        pub fn set(&self, offset: u32, value: Option<FuncRef>) -> Result<(), Error> {
            let mut buffer = self.buffer.borrow_mut();
            let buffer_len = buffer.len();
            let table_elem = buffer.get_mut(offset as usize).ok_or_else(|| {
                Error::Table(format!(
                    "trying to update table item with index {} when there are only {} items",
                    offset, buffer_len
                ))
            })?;
            *table_elem = value;
            Ok(())
        }
    }

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