awesome/lib/gears/object/properties.lua

---------------------------------------------------------------------------
--- An helper module to map userdata __index and __newindex entries to
-- lua classes.
--
-- @author Emmanuel Lepage-Vallee <elv1313@gmail.com>
-- @copyright 2016 Emmanuel Lepage-Vallee
-- @release @AWESOME_VERSION@
-- @module gears.object.properties
---------------------------------------------------------------------------

local object = {}

local properties = setmetatable({}, { __mode = 'k' })

local function cobj_register(cobj)
    local fallback = {}

    function fallback:rawset(_, prop, val)
        fallback[prop] = val
    end

    function fallback:rawget(_, prop)
        return fallback[prop]
    end

    properties[cobj] = fallback
    return fallback
end

--- Add the missing properties handler to a CAPI object such as client/tag/screen
-- Valid args:
--
-- * **getter**: A smart getter (handle property getter itself)
-- * **getter_fallback**: A dumb getter method (don't handle individual property getter)
-- * **getter_class**: A module with individual property getter/setter
-- * **getter_prefix**: A special getter prefix (like "get" or "get_" (default))
-- * **setter**: A smart setter (handle property setter itself)
-- * **setter_fallback**: A dumb setter method (don't handle individual property setter)
-- * **setter_class**: A module with individual property getter/setter
-- * **setter_prefix**: A special setter prefix (like "set" or "set_" (default))
-- * **auto_emit**: Emit "property::___" automatically (default: false). This is
--     ignored when setter_fallback is set or a setter is found
--
-- @param class A standard luaobject derived object
-- @tparam[opt={}] table args A set of accessors configuration parameters
function object.capi_index_fallback(class, args)
    args = args or {}

    local getter_prefix = args.getter_prefix or "get_"
    local setter_prefix = args.setter_prefix or "set_"

    local getter = args.getter or function(cobj, prop)
        -- Look for a getter method
        if args.getter_class and args.getter_class[getter_prefix..prop] then
            return args.getter_class[getter_prefix..prop](cobj)
        end

        -- Make sure something like c:a_mutator() works
        if args.getter_class and args.getter_class[prop] then
            return args.getter_class[prop]
        end

        -- In case there is already a "dumb" getter like `awful.tag.getproperty'
        if args.getter_fallback then
            return args.getter_fallback(cobj, prop)
        end

        local fallback = properties[cobj] or cobj_register(cobj)

        -- Use the fallback property table
        return fallback[prop]
    end

    local setter = args.setter or function(cobj, prop, value)
        -- Look for a setter method
        if args.setter_class and args.setter_class[setter_prefix..prop] then
            return args.setter_class[setter_prefix..prop](cobj, value)
        end

        -- In case there is already a "dumb" setter like `awful.client.property.set'
        if args.setter_fallback then
            return args.setter_fallback(cobj, prop, value)
        end

        local fallback = properties[cobj] or cobj_register(cobj)

        -- Use the fallback property table
        fallback[prop] = value

        -- Emit the signal
        if args.auto_emit then
            cobj:emit_signal("property::"..prop, value)
        end
    end

    -- Attach the accessor methods
    class.set_index_miss_handler(getter)
    class.set_newindex_miss_handler(setter)
end

return setmetatable( object, {__call = function(_,...) object.capi_index_fallback(...) end})

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