Multiple geometry columns

library(sf)
sf <- st_sf(a = c("x", "y"), geom = st_sfc(st_point(3:4), st_point(3:4)))
sf[["geom2"]] = st_sfc(st_point(3:4), st_point(3:4))
sf
Simple feature collection with 2 features and 1 field
Active geometry column: geom
geometry type:  POINT
dimension:      XY
bbox:           xmin: 3 ymin: 4 xmax: 3 ymax: 4
epsg (SRID):    NA
proj4string:    NA
  a        geom       geom2
1 x POINT (3 4) POINT (3 4)
2 y POINT (3 4) POINT (3 4)

should encode.sf apply to multiple columns?

sfGeometryColumn.sf <- function(sf) names( which( sapply( sf, function(x) inherits(x, "sfc") ) ) )