Macro decl_extension 

macro_rules! decl_extension {
    (
		$( #[ $attr:meta ] )*
		$vis:vis struct $ext_name:ident ($inner:ty);
		$(
			impl $ext_name_impl:ident {
				$(
					$impls:tt
				)*
			}
		)*
	) => { ... };
    (
		$( #[ $attr:meta ] )*
		$vis:vis struct $ext_name:ident;
	) => { ... };
}

Macro for declaring an extension that usable with Extensions.

The extension will be an unit wrapper struct that implements Extension, Deref and DerefMut. The wrapped type is given by the user.

Example

decl_extension! {
    /// Some test extension
    struct TestExt(String);
}

The Extension trait provides hooks that are called when starting, committing or rolling back a transaction. These can be implemented with the macro as well:

decl_extension! {
    /// Some test extension
    struct TestExtWithCallback(String);

    impl TestExtWithCallback {
        fn start_transaction(&mut self, ty: TransactionType) {
            // do something cool
        }

        // The other methods `commit_transaction` and `rollback_transaction` can also
        // be implemented in the same way.
    }
}