Allocations in GapGroupHomomorphism from a julia function

[simonbrandhorst]

Wrapping something in a gap homomorphism increases allocations considerably.
Is this unavoidable?

julia> L = root_lattice(:E,8);

julia> G,sv = Oscar._isometry_group_via_decomposition(L);

julia> w = similar(sv[1]);

julia> n = length(sv)
240

julia> Sn = symmetric_group(n);

julia> act_func(g) = perm(Sn, Oscar._as_perm(w, matrix(g), sv))
act_func (generic function with 1 method)

julia> fG = hom(G, Sn, act_func)
Group homomorphism
  from matrix group of degree 8 over ZZ
  to symmetric group of degree 240

julia> g = prod(gens(G));

julia> sort!(sv, lt=Hecke._isless);

julia> @b act_func(g)
60.646 μs (7 allocs: 4.594 KiB)

julia> @b fG(g)
70.468 μs (89 allocs: 8.227 KiB)

So in this case the number of allocations almost doubles.

[simonbrandhorst]

@fingolfin @ThomasBreuer