GTKD Cairo get pixel color

[TheDGuy via Digitalmars-d-learn]

On Tuesday, 5 January 2016 at 16:43:00 UTC, Basile B. wrote:
> On Tuesday, 5 January 2016 at 16:25:01 UTC, TheDGuy wrote:
>> But how do i know which line or column my pixel is in?
> - study D operator overloading, I've given you the solution.
>
>> And what is 't' in 'opIndexAssign'?
> - t is what you want to assign. It can be an uint or maybe a 
> float[4]. Look at my bitmap class.

Okay, but what is this?

"import iz.memory, iz.streams, iz.properties;"

I dont' understand what "MemoryStream" is?