Can someone tell me why the following generates an error? The 'overlay' description in the 'raster' package suggests the single-layer object should recycle as needed...

Thanks!
Kevin

> r <- raster(ncol=10, nrow=10)
> r <- init(r, fun=runif)
> stack_r=stack(r,r)

> overlay(stack_r,r,fun=sum)
Error in function (classes, fdef, mtable)  : 
  unable to find an inherited method for function "overlay", for signature "RasterStack", "RasterLayer"

Seems to me that the command above should be able to replicate:

> stack_r+r
class       : RasterBrick 
filename    :  
nlayers     : 2 
nrow        : 10 
ncol        : 10 
ncell       : 100 
projection  : +proj=longlat +datum=WGS84 +ellps=WGS84 +towgs84=0,0,0 
min value   : 0.011 0.011 
max value   : 2 2 
extent      : -180, 180, -90, 90  (xmin, xmax, ymin, ymax)
resolution  : 36, 18  (x, y)

I need single-layer objects used as arguments within 'overlay' to recycle for more complex functions that include raster stacks...
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