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diff --git a/Source/Initialization/InjectorPosition.H b/Source/Initialization/InjectorPosition.H
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+#ifndef INJECTOR_POSITION_H_
+#define INJECTOR_POSITION_H_
+
+#include <AMReX_Gpu.H>
+#include <AMReX_Dim3.H>
+#include <AMReX_Utility.H>
+
+// struct whose getPositionUnitBox returns x, y and z for a particle with
+// random distribution inside a unit cell.
+struct InjectorPositionRandom
+{
+    AMREX_GPU_HOST_DEVICE
+    amrex::XDim3
+    getPositionUnitBox (int i_part, int ref_fac=1) const noexcept
+    {
+        return amrex::XDim3{amrex::Random(), amrex::Random(), amrex::Random()};
+    }
+};
+
+// struct whose getPositionUnitBox returns x, y and z for a particle with
+// regular distribution inside a unit cell.
+struct InjectorPositionRegular
+{
+    InjectorPositionRegular (amrex::Dim3 const& a_ppc) noexcept : ppc(a_ppc) {}
+
+    // i_part: particle number within the cell, required to evenly space
+    // particles within the cell.
+    // ref_fac: the number of particles evenly-spaced within a cell 
+    // is a_ppc*(ref_fac**AMREX_SPACEDIM).
+    AMREX_GPU_HOST_DEVICE
+    amrex::XDim3
+    getPositionUnitBox (int i_part, int ref_fac=1) const noexcept
+    {
+        int nx = ref_fac*ppc.x;
+        int ny = ref_fac*ppc.y;
+#if (AMREX_SPACEDIM == 3)
+        int nz = ref_fac*ppc.z;
+#else
+        int nz = 1;
+#endif
+        int ix_part = i_part/(ny*nz);  // written this way backward compatibility
+        int iz_part = (i_part-ix_part*(ny*nz)) / ny;
+        int iy_part = (i_part-ix_part*(ny*nz)) - ny*iz_part;
+        return amrex::XDim3{(0.5+ix_part)/nx, (0.5+iy_part)/ny, (0.5+iz_part) / nz};
+    }
+private:
+    amrex::Dim3 ppc;
+};
+
+// Base struct for position injector. 
+// InjectorPosition contains a union (called Object) that holds any one 
+// instance of: 
+// - InjectorPositionRandom : to generate random distribution;
+// - InjectorPositionRegular: to generate regular distribution.
+// The choice is made at runtime, depending in the constructor called.
+// This mimics virtual functions, except the struct is stored in managed memory
+// and member functions are made __host__ __device__ to run on CPU and GPU.
+// This struct inherits from amrex::Gpu::Managed to provide new and delete
+// operators in managed memory when running on GPU. Nothing special on CPU.
+struct InjectorPosition
+    : public amrex::Gpu::Managed
+{
+    // This constructor stores a InjectorPositionRandom in union object.
+    InjectorPosition (InjectorPositionRandom* t,
+                      amrex::Real a_xmin, amrex::Real a_xmax,
+                      amrex::Real a_ymin, amrex::Real a_ymax,
+                      amrex::Real a_zmin, amrex::Real a_zmax)
+        : type(Type::random),
+          object(t),
+          xmin(a_xmin), xmax(a_xmax),
+          ymin(a_ymin), ymax(a_ymax),
+          zmin(a_zmin), zmax(a_zmax)
+    { }
+
+    // This constructor stores a InjectorPositionRegular in union object.
+    InjectorPosition (InjectorPositionRegular* t,
+                      amrex::Real a_xmin, amrex::Real a_xmax,
+                      amrex::Real a_ymin, amrex::Real a_ymax,
+                      amrex::Real a_zmin, amrex::Real a_zmax,
+                      amrex::Dim3 const& a_ppc)
+        : type(Type::regular),
+          object(t, a_ppc),
+          xmin(a_xmin), xmax(a_xmax),
+          ymin(a_ymin), ymax(a_ymax),
+          zmin(a_zmin), zmax(a_zmax)
+    { }
+
+    // Explicitly prevent the compiler from generating copy constructors
+    // and copy assignment operators.
+    InjectorPosition (InjectorPosition const&) = delete;
+    InjectorPosition (InjectorPosition&&) = delete;
+    void operator= (InjectorPosition const&) = delete;
+    void operator= (InjectorPosition &&) = delete;
+
+    std::size_t sharedMemoryNeeded () const noexcept { return 0; }
+
+    // call getPositionUnitBox from the object stored in the union
+    // (the union is called Object, and the instance is called object).
+    AMREX_GPU_HOST_DEVICE
+    amrex::XDim3
+    getPositionUnitBox (int i_part, int ref_fac=1) const noexcept
+    {
+        switch (type)
+        {
+        case Type::regular:
+        {
+            return object.regular.getPositionUnitBox(i_part, ref_fac);
+        }
+        default:
+        {
+            return object.random.getPositionUnitBox(i_part, ref_fac);
+        }
+        };
+    }
+
+    // bool: whether position specified is within bounds.
+    AMREX_GPU_HOST_DEVICE
+    bool
+    insideBounds (amrex::Real x, amrex::Real y, amrex::Real z) const noexcept
+    {
+        return (x < xmax and x >= xmin and
+                y < ymax and y >= ymin and
+                z < zmax and z >= zmin);
+    }
+
+private:
+    enum struct Type { random, regular };
+    Type type;
+
+    // An instance of union Object constructs and stores any one of
+    // the objects declared (random or regular).
+    union Object {
+        Object (InjectorPositionRandom*) noexcept : random() {}
+        Object (InjectorPositionRegular*, amrex::Dim3 const& a_ppc) noexcept
+            : regular(a_ppc) {}
+        InjectorPositionRandom random;
+        InjectorPositionRegular regular;
+    };
+    Object object;
+
+    amrex::Real xmin, xmax;
+    amrex::Real ymin, ymax;
+    amrex::Real zmin, zmax;
+};
+
+#endif