btw for my immediate needs i replace second delegate with value
i.e. remove "lazy" from declaration and remove "()" in return

so ifThrown loose some generity

nothrow
CommonType!(T1, T2) ifThrown(E : Throwable = Exception, T1, T2)
                            (lazy scope T1 expression, scope T2 expression2)
...
    try
        return expression();
    catch (E)
        return expression2;