function changecomp(vec, setter, comps, op) {
    return new ChangeCompExpr(vec, expr_1.wrapInValue(setter), comps, op);
}
change the components of a vector
@param vec the vector to augment components of
@param setter the vector (or float, if only one component is changed) for
how to change the components
@param comps string representing the components to change (e.g. `"xy"` or
`"r"` or `"stpq"`.)
@param op optionally perform an operation on the original component
(defaults to no operation, just assigning that component to a new value)