put gcn inputs check behind function barrier (#261)

Author: CarloLucibello

src/layers/conv.jl

@@ -74,14 +74,24 @@ function GCNConv(ch::Pair{Int, Int}, σ = identity;
     GCNConv(W, b, σ, add_self_loops, use_edge_weight)
 end
 
-function (l::GCNConv)(g::GNNGraph, x::AbstractMatrix{T},
-                      edge_weight::EW = nothing) where
-    {T, EW <: Union{Nothing, AbstractVector}}
-    @assert !(g isa GNNGraph{<:ADJMAT_T} && edge_weight !== nothing) "Providing external edge_weight is not yet supported for adjacency matrix graphs"
+check_gcnconv_input(g::GNNGraph{<:ADJMAT_T}, edge_weight::AbstractVector) = 
+    throw(ArgumentError("Providing external edge_weight is not yet supported for adjacency matrix graphs"))
 
-    if edge_weight !== nothing
-        @assert length(edge_weight)==g.num_edges "Wrong number of edge weights (expected $(g.num_edges) but given $(length(edge_weight)))"
+function check_gcnconv_input(g::GNNGraph, edge_weight::AbstractVector)
+    if length(edge_weight) !== g.num_edges 
+        throw(ArgumentError("Wrong number of edge weights (expected $(g.num_edges) but given $(length(edge_weight)))"))
     end
+end
+
+check_gcnconv_input(g::GNNGraph, edge_weight::Nothing) = nothing
+
+
+function (l::GCNConv)(g::GNNGraph, 
+                      x::AbstractMatrix{T},
+                      edge_weight::EW = nothing
+                      ) where {T, EW <: Union{Nothing, AbstractVector}}
+
+    check_gcnconv_input(g, edge_weight)
 
     if l.add_self_loops
         g = add_self_loops(g)