Strange casting error when using lamdas

[Robert M. Münch]

I have very strange casting error I don't understand:

alias typeof(windows_message_streams[WM_MOUSEMOVE].filter!(win => 
(win.wParam & MK_LBUTTON))) WM_MOUSEMOVE_LBUTTON_TYPE;
WM_MOUSEMOVE_LBUTTON_TYPE WM_MOUSEMOVE_LBUTTON_STREAM;
pragma(msg,typeof(WM_MOUSEMOVE_LBUTTON_STREAM));

>> FilterObservable!(__lambda39, SubjectObject!(OS_State))

WM_MOUSEMOVE_LBUTTON_STREAM = 
cast(WM_MOUSEMOVE_LBUTTON_TYPE)(windows_message_streams[WM_MOUSEMOVE].filter!(win 
=> (win.wParam & MK_LBUTTON)));
pragma(msg,typeof(wstreams[WM_MOUSEMOVE].filter!(win => (win.wParam & 
MK_LBUTTON))));

>> FilterObservable!(__lambda7, SubjectObject!(OS_State))

..\..\gui.d(317,104): Error: cannot cast expression 
filter(windows_message_streams[512u]) of type 
FilterObservable!(__lambda6, SubjectObject!(OS_State)) to 
FilterObservable!(__lambda39, SubjectObject!(OS_State)) because of 
different sizes
FilterObservable!(__lambda7, SubjectObject!(OS_State))

My code worked in the past but now it doesn't and I don't know why. I 
don't understand the "because of different sizes" message.

It looks like I have to explicitly create a lambda and re-use it. But 
how to do that?

-- 
Robert M. Münch
http://www.saphirion.com
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