how can i pass a range, and not text?

because i would like to use my custom function in dragging and filling. this way the range is auto calculated by the sheets.

i mean =dosomething(B2) , and i drag and fill that cell to 5 cells to right, and google sheets fills automatically =dosomething(C2) dosomething(D2) dosomething(E2) dosomething(F2) dosomething(G2)

but when you pass the range as a text, the drag and fill does not work ...