Assigning datasource to self



I am following the ‘Quick Start Quide’ and after resolving the first Mach-O linker issue I get a warning while assigning datasource to self. Xcode throws me a: /PostViewController.m:77:23: Assigning to ‘id<SChartDatasource>’ from incompatible type ‘PostViewController *const __strong’. 

Is there anyway around the warning? - apart from casting it as:

 _chart.datasource = (id<SChartDatasource>)self;


The reason I ask is that I was wondering if I was doing something wrong, since otherwise the sample code would (should?) display a warning.