Trait HashKeyDispatcher 

pub trait HashKeyDispatcher: Sized {
    type Output;

    // Required methods
    fn dispatch_impl<K: HashKey>(self) -> Self::Output;
    fn data_types(&self) -> &[DataType];

    // Provided methods
    fn dispatch(self) -> Self::Output { ... }
    fn dispatch_by_key_size<T: NullBitmap>(self) -> Self::Output { ... }
}

A trait to help to dynamically dispatch HashKey template.

Suppose you want to build a trait object of type T, whose underlying implementation is S<K: HashKey>, you can implement a HashKeyDispatcher with Output=T. Then you can use dispatch_by_kind to build T directly without working with generic argument K.

Required Associated Types

type Output

Required Methods

fn dispatch_impl<K: HashKey>(self) -> Self::Output

fn data_types(&self) -> &[DataType]

The data types used to build the hash key.

Provided Methods

fn dispatch(self) -> Self::Output

Based on the number of group keys and total size of group keys, we decide:

1. What bitmap to use for representing null values in group keys.
2. What key type to store group keys in.

fn dispatch_by_key_size<T: NullBitmap>(self) -> Self::Output

All data types will be stored in a single HashKey. We use Key<N> for fixed size keys, KeySerialized for variable length keys.

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementors