avoid assigning storage for nothing situation

src/Denudation/Abstract.jl

@@ -14,7 +14,7 @@ abstract type DenudationType end
 FIXME Computes the denudation for a single time-step, given denudation parameters `param` and a simulation state `state`. `param` should have a `DenudationType` type and `state` should contain the `height` property and `sealevel`.
 """
 function denudation(input)
-    denudation_mass::Array{typeof(1.0u"m/kyr"),2} = Array{typeof(1.0u"m/kyr")}(undef, input.box.grid_size...)
+    denudation_mass::Union{Array{typeof(1.0u"m/kyr"),2}, Nothing} = Array{typeof(1.0u"m/kyr")}(undef, input.box.grid_size...)
 
     function (state, water_depth, slope)
         for idx in CartesianIndices(state.ca)
@@ -24,7 +24,13 @@ function denudation(input)
             end
 
             if water_depth[idx] >= 0
-                (denudation_mass[idx]) = denudation(input.box, input.denudation, water_depth[idx], slope[idx], input.facies[f])
+
+                if denudation(input.box, input.denudation, water_depth[idx], slope[idx], input.facies[f]) !== nothing
+                   (denudation_mass[idx]) = denudation(input.box, input.denudation, water_depth[idx], slope[idx], input.facies[f])
+                else
+                    denudation_mass = nothing
+                end
+
             end
         end
         return denudation_mass
@@ -46,9 +52,13 @@ end
 FIXME
 """
 function redistribution(input)
-    redistribution_mass::Array{typeof(1.0u"m/kyr"),2} = Array{typeof(1.0u"m/kyr")}(undef, input.box.grid_size...)
+        redistribution_mass::Union{Array{typeof(1.0u"m/kyr"),2}, Nothing} = Array{typeof(1.0u"m/kyr")}(undef, input.box.grid_size...)
     function (state, water_depth, denudation_mass)
+        if redistribution(input.box, input.denudation, denudation_mass, water_depth) !== nothing
         redistribution_mass = redistribution(input.box, input.denudation, denudation_mass, water_depth)
+        else
+        redistribution_mass = nothing
+        end
         return redistribution_mass
     end
 end

src/Denudation/DissolutionMod.jl

@@ -60,7 +60,7 @@ function denudation(::Box{BT}, p::Dissolution, water_depth, slope, facies) where
 end
 
 function redistribution(box::Box{BT}, p::Dissolution, denudation_mass, water_depth) where {BT<:Boundary}
-    return denudation_mass .* 0
+    return nothing
 end
 
 end

src/Denudation/EmpiricalDenudationMod.jl

@@ -42,7 +42,7 @@ function denudation(::Box, p::EmpiricalDenudation, water_depth, slope, facies)
 end
 
 function redistribution(::Box, p::EmpiricalDenudation, denudation_mass, water_depth)
-    return denudation_mass .* 0
+    return nothing
 end
 
 end

src/Denudation/NoDenudationMod.jl

@@ -17,7 +17,7 @@ function denudation(box::Box, p::NoDenudation, water_depth::Any, slope, facies)
 end
 
 function redistribution(box::Box, p::NoDenudation, denudation_mass, water_depth)
-    return denudation_mass .* 0
+    return nothing
 end
 
 end

src/Model/WithDenudation.jl

@@ -53,8 +53,8 @@ end
 
 struct OutputFrame
     production::Array{typeof(1.0u"m/Myr"),3}
-    denudation::Array{typeof(1.0u"m/Myr"),2}
-    redistribution::Array{typeof(1.0u"m/Myr"),2}
+    denudation::Union{Array{typeof(1.0u"m/Myr"),2},Nothing}
+    redistribution::Union{Array{typeof(1.0u"m/Myr"),2},Nothing}
 end
 # FIXME: deduplicate
 mutable struct State
@@ -138,8 +138,12 @@ function updater(input)
 
     function update(state, Δ::DenudationFrame)
         # FIXME: implement
+        if Δ.denudation !== nothing
         state.height .+= Δ.denudation .* input.time.Δt
+        end
+        if Δ.redistribution !== nothing
         state.height .-= Δ.redistribution .* input.time.Δt
+        end
         state.time += input.time.Δt
     end
 
@@ -187,24 +191,39 @@ function main(input::Input, output::String)
         attr["subsidence_rate"] = input.subsidence_rate |> in_units_of(u"m/Myr")
         println("Subsidence rate saved successfully.")
 
+        box = input.box
+        results = map(stack_frames, partition(run_model(input, box), input.time.write_interval))
+        testframe = first(results)
 
         n_facies = length(input.facies)
         ds = create_dataset(fid, "sediment", datatype(Float64),
             dataspace(input.box.grid_size..., n_facies, input.time.steps),
             chunk=(input.box.grid_size..., n_facies, 1))
-        denudation = create_dataset(fid, "denudation", datatype(Float64),
-            dataspace(input.box.grid_size..., input.time.steps),
-            chunk=(input.box.grid_size..., 1))
-        redistribution = create_dataset(fid, "redistribution", datatype(Float64),
-            dataspace(input.box.grid_size..., input.time.steps),
-            chunk=(input.box.grid_size..., 1))
-        box = input.box
 
-        results = map(stack_frames, partition(run_model(input, box), input.time.write_interval))
+        denudation = nothing
+        if testframe.denudation !== nothing
+            denudation = create_dataset(fid, "denudation", datatype(Float64),
+                dataspace(input.box.grid_size..., input.time.steps),
+                chunk=(input.box.grid_size..., 1))
+        end
+
+        redistribution = nothing
+        if testframe.redistribution !== nothing
+            redistribution = create_dataset(fid, "redistribution", datatype(Float64),
+                dataspace(input.box.grid_size..., input.time.steps),
+                chunk=(input.box.grid_size..., 1))
+        end
+
         for (step, frame) in enumerate(take(results, n_writes))
             ds[:, :, :, step] = frame.production |> in_units_of(u"m/Myr")
-            denudation[:, :, step] = frame.denudation |> in_units_of(u"m/kyr")
-            redistribution[:, :, step] = frame.redistribution |> in_units_of(u"m/kyr")
+
+            if denudation !== nothing
+                denudation[:, :, step] = frame.denudation |> in_units_of(u"m/kyr")
+            end
+
+            if redistribution !== nothing
+                redistribution[:, :, step] = frame.redistribution |> in_units_of(u"m/kyr")
+            end
         end
     end
 end