By that logic, shouldn't you be creating a var for the expression_argument() return?
Did you compare writing in different ways and reading it later? This specific style confuses me the most, because I have to mentally connect an assignment with a flow control, because there is no guarantee that a following if() will not use a different variable or it was not shadowed, misnamed, etc. And given that, at once I see x2-3 lines less than usual.