Base.similar for <:AbstractGrids

src/RingGrids/RingGrids.jl

@@ -70,4 +70,5 @@ include("octahealpix.jl")
 include("quadrature_weights.jl")
 include("interpolation.jl")
 include("show.jl")
+include("similar.jl")
 end

src/RingGrids/similar.jl

@@ -0,0 +1,24 @@
+# todo this should be replaced by general broadcasting for <: AbstractGrid
+for Grid in (:FullGaussianGrid, :FullClenshawGrid, :FullHEALPixGrid, :FullOctaHEALPixGrid,
+            :OctahedralGaussianGrid, :OctahedralClenshawGrid, :HEALPixGrid,
+            :OctaHEALPixGrid)
+    @eval begin
+
+        function Base.similar(G::$Grid)
+            return $Grid{eltype(G)}(undef,G.nlat_half)
+        end
+
+        function Base.similar(G::$Grid,::Type{T}) where T
+            return $Grid{T}(undef,G.nlat_half)
+        end
+
+        function Base.similar(G::$Grid,nlat_half::Integer)
+            return $Grid{eltype(G)}(undef,nlat_half)
+        end
+
+        function Base.similar(G::$Grid,::Type{T},nlat_half::Integer) where T
+            return $Grid{T}(undef,nlat_half)
+        end
+
+    end
+end

src/SpeedyTransforms/spectral_transform.jl

@@ -551,13 +551,13 @@ end
 """
 $(TYPEDSIGNATURES)
 Spectral transform (grid to spectral) `map` to `grid(map)` to execute `spectral(map::AbstractGrid;kwargs...)`."""
-function spectral(  map::Grid,                      # gridded field
-                    S::SpectralTransform{NF},       # spectral transform struct
-                    ) where {Grid<:AbstractGrid,NF} # number format NF
+function spectral(  map::AbstractGrid,          # gridded field
+                    S::SpectralTransform{NF},   # spectral transform struct
+                    ) where NF                  # number format NF
 
-    map_NF = Grid{NF}(map)                          # convert map to NF
+    map_NF = similar(map,NF)                    # convert map to NF
+    copyto!(map_NF,map)
 
-    # always use one more l for consistency with vector quantities
     alms = LowerTriangularMatrix{Complex{NF}}(undef,S.lmax+1,S.mmax+1)
-    return spectral!(alms,map_NF,S)                # in-place version
+    return spectral!(alms,map_NF,S)             # in-place version
 end