Using

ADL (no namespace prefix needed)

using pfc::DiscreteField;
DiscreteField<double, 3> field({32,32,32}, {0,0,0},
                                {0.0,0.0,0.0}, {1.0,1.0,1.0});
 
// ADL finds pfc::interpolate automatically
double& val = interpolate(field, {10.5, 15.3, 8.2});