get_osm_data <- function( city, amenity ) {
  # bound box for city
  bb <- getbb(city, format_out = "sf_polygon")
  # create overpass query for the amenity
  v <- unlist(strsplit(amenity, ':'))
  q <- opq(bb) %>% add_osm_feature(key = v[1], value=v[2])
  # get the data
  return <- osmdata_sf(q, quiet=F)
}

^{Created on 2019-08-14 by the reprex package (v0.3.0)}