lldb error: use of undeclared identifier
===

Anyone know whats going on here:

    @implementation Test
    {
        NSData *_data;
    }
    
    - (id)initWithData:(NSData *)data
    {
        self = [super init];
        if (self)
        {
            _data = data;
        } 
        return self;  // BREAKPOINT HERE
    }

From lldb:

    (lldb) p data
    (NSData *) $1 = 0x07f911e0 30308 bytes
    (lldb) p _data
    error: use of undeclared identifier '_data'
    error: 1 errors parsing expression

Why can't I view `_data`?