RFC: extend unsafe_assign to work for any isbits type, add pointer_from_objref

base/exports.jl

@@ -1127,6 +1127,7 @@ export
     unsafe_ref,
     unsafe_assign,
     unsafe_pointer_to_objref,
+    pointer_from_objref,
 
 # Macros
     @str,

base/pointer.jl

@@ -38,8 +38,9 @@ unsafe_assign(p::Ptr{Any}, x::ANY, i::Integer) = pointerset(p, x, int(i))
 unsafe_assign{T}(p::Ptr{T}, x, i::Integer) = pointerset(p, convert(T, x), int(i))
 unsafe_assign{T}(p::Ptr{T}, x) = unsafe_assign(p, convert(T,x), 1)
 
-# convert a raw Ptr to an object reference
+# convert a raw Ptr to an object reference, and vice-versa
 unsafe_pointer_to_objref(p::Ptr) = pointertoref(unbox(Ptr{Void},p))
+pointer_from_objref(x::Any) = ccall(:jl_value_ptr, Ptr{Void}, (Any,), x)
 
 integer(x::Ptr) = convert(Uint, x)
 unsigned(x::Ptr) = convert(Uint, x)

doc/manual/calling-c-and-fortran-code.rst

@@ -321,12 +321,15 @@ If T is Any, then the referenced memory is assumed to contain some
 that the object was always visible to the garbage collector (pointers do not
 count, but the new object does) to ensure the memory is not prematurely freed.
 Note that if the object was not originally allocated by Julia, the new object
-will never be finalized by Julia's garbage collector.  If the `Ptr` itself
+will never be finalized by Julia's garbage collector.  If the ``Ptr`` itself
 is actually a ``jl_value_t*``, it can be converted back to a Julia object
-reference by ``unsafe_pointer_to_objref(ptr)``.
+reference by ``unsafe_pointer_to_objref(ptr)``.  [Julia values ``v``
+can be converted to ``jl_value_t*`` pointers (``Ptr{Void}``) by calling
+``pointer_from_objref(v)``.]
 
 The reverse operation (writing data to a Ptr{T}), can be performed using
-``unsafe_assign(ptr, value, [index])``.
+``unsafe_assign(ptr, value, [index])``.  Currently, this is only supported
+for bitstypes or other pointer-free (``isbits``) immutable types.
 
 Any operation that throws an error is probably currently unimplemented
 and should be posted as a bug so that it can be resolved.

src/intrinsics.cpp

@@ -404,7 +404,7 @@ static Value *emit_pointerref(jl_value_t *e, jl_value_t *i, jl_codectx_t *ctx)
     Value *thePtr = auto_unbox(e,ctx);
     Value *idx = emit_unbox(T_size, T_psize, emit_unboxed(i, ctx));
     Value *im1 = builder.CreateSub(idx, ConstantInt::get(T_size, 1));
-    if (!jl_is_bitstype(ety)) {
+    if (!jl_isbits(ety)) {
         if (ety == (jl_value_t*)jl_any_type)
             return builder.CreateLoad(builder.CreateGEP(
                         builder.CreateBitCast(thePtr, jl_ppvalue_llvmt),
@@ -438,7 +438,7 @@ static Value *emit_pointerset(jl_value_t *e, jl_value_t *x, jl_value_t *i, jl_co
     jl_value_t *xty = expr_type(x, ctx);    
     if (!jl_subtype(xty, ety, 0))
         jl_error("pointerset: type mismatch in assign");
-    if (!jl_is_bitstype(ety)) {
+    if (!jl_isbits(ety)) {
         jl_error("pointerset: invalid pointer type"); //ety = (jl_value_t*)jl_any_type;
     }
     if ((jl_datatype_t*)expr_type(i, ctx) != jl_long_type) {

test/core.jl

@@ -475,6 +475,20 @@ end
 
 @test unsafe_pointer_to_objref(ccall(:jl_call1, Ptr{Void}, (Any,Any),
                                      x -> x+1, 314158)) == 314159
+@test unsafe_pointer_to_objref(pointer_from_objref(e+pi)) == e+pi
+
+immutable FooBar
+    foo::Int
+    bar::Int
+end
+begin
+    local X, p
+    X = FooBar[ FooBar(3,1), FooBar(4,4) ]
+    p = convert(Ptr{FooBar}, X)
+    @test unsafe_ref(p, 2) == FooBar(4,4)
+    unsafe_assign(p, FooBar(7,3), 1)
+    @test X[1] == FooBar(7,3)
+end
 
 # issue #1287, combinations of try, catch, return
 begin