AccessorFacade

A Raku method trait to turn indivdual get/set subroutines into a single read/write object attribute.

Description

This module was initially designed to reduce the boiler plate code in a native library binding that became something like:

    class Shout is repr('CPointer') {

        sub shout_set_host(Shout, Str) returns int32 is native('libshout') { * }
        sub shout_get_host(Shout) returns Str is native('libshout') { * }

        method host() is rw {
            Proxy.new(
                FETCH => sub ($) {
                    shout_get_host(self);
                },
                STORE   =>  sub ($, $host is copy ) {
                    explicitly-manage($host);
                    shout_set_host(self, $host);
                }
            );
        }

        ...

    }

That is the library API provides a sort of "object oriented" mechanism to set and get attributes on an opaque object instance that was returned by another "constructor" function. Because the object is an opaque CPointer it can only have subroutines and methods and not private data or attributes. The intent of the code is to provide fake "attributes" with rw methods (which is similar to how public rw attributes are provided.)

The above code will be reduced with the use of AccessorFacade to:

    class Shout is repr('CPointer') {

        sub shout_set_host(Shout, Str) returns int32 is native('libshout') { * }
        sub shout_get_host(Shout) returns Str is native('libshout') { * }

        method host() is rw is accessor-facade(&shout_get_host, &shout_set_host) { }

        ...
    }

The named argument style is also supported so the method could be written as:

    method host() is rw is accessor-facade(getter => &shout_get_host, setter => &shout_set_host) { }

if that proves more suitable.

(The call to explicitly manage is omitted for simplicity but how this is achieved is described in the documentation.) Libshout has a significant number of these get/set pairs so there is a reduction of typing, copy and paste and hopefully programmer error.

Whilst this was designed primarily to work with a fixed native API, it is possible that it could be used to provide an OO facade to a plain Raku procedural library. The only requirement that there is a getter subroutine that accepts an object as its first argument and returns the attribute value and a setter subroutine that accepts the object and the value to be set (it may return a value to indicate success - how this is handled is descibed in the documentation.)

Installation

Assuming you have a working Rakudo installation you should be able to install this with zef :

# From the source directory

zef install .

# Remote installation

zef install AccessorFacade

Support

Suggestions/patches are welcomed via github at:

https://github.com/jonathanstowe/AccessorFacade/issues

Licence

This is free software.

Please see the LICENCE file in the distribution

© Jonathan Stowe 2015 - 2021