refpointer.jl

# This file is a part of Julia. License is MIT: https://julialang.org/license

"""
    Ref{T}

An object that safely references data of type `T`. This type is guaranteed to point to
valid, Julia-allocated memory of the correct type. The underlying data is protected from
freeing by the garbage collector as long as the `Ref` itself is referenced.

In Julia, `Ref` objects are dereferenced (loaded or stored) with `[]`.

Creation of a `Ref` to a value `x` of type `T` is usually written `Ref(x)`.
Additionally, for creating interior pointers to containers (such as Array or Ptr),
it can be written `Ref(a, i)` for creating a reference to the `i`-th element of `a`.

When passed as a `ccall` argument (either as a `Ptr` or `Ref` type), a `Ref` object will be
converted to a native pointer to the data it references.

There is no invalid (NULL) `Ref` in Julia, but a `C_NULL` instance of `Ptr` can be passed to
a `ccall` Ref argument.

# Use in broadcasting
`Ref` is sometimes used in broadcasting in order to treat the referenced values as a scalar:

```jldoctest
julia> isa.(Ref([1,2,3]), [Array, Dict, Int])
3-element BitArray{1}:
 1
 0
 0
```
"""
Ref

# C NUL-terminated string pointers; these can be used in ccall
# instead of Ptr{Cchar} and Ptr{Cwchar_t}, respectively, to enforce
# a check for embedded NUL chars in the string (to avoid silent truncation).
if Int === Int64
    primitive type Cstring  64 end
    primitive type Cwstring 64 end
else
    primitive type Cstring  32 end
    primitive type Cwstring 32 end
end

### General Methods for Ref{T} type

eltype(x::Type{<:Ref{T}}) where {T} = @isdefined(T) ? T : Any
convert(::Type{Ref{T}}, x::Ref{T}) where {T} = x
size(x::Ref) = ()
axes(x::Ref) = ()
length(x::Ref) = 1
ndims(x::Ref) = 0
ndims(::Type{<:Ref}) = 0
iterate(r::Ref) = (r[], nothing)
iterate(r::Ref, s) = nothing
IteratorSize(::Type{<:Ref}) = HasShape{0}()

# create Ref objects for general object conversion
unsafe_convert(::Type{Ref{T}}, x::Ref{T}) where {T} = unsafe_convert(Ptr{T}, x)
unsafe_convert(::Type{Ref{T}}, x) where {T} = unsafe_convert(Ptr{T}, x)

convert(::Type{Ref{T}}, x) where {T} = RefValue{T}(x)

### Methods for a Ref object that is backed by an array at index i
struct RefArray{T,A<:AbstractArray{T},R} <: Ref{T}
    x::A
    i::Int
    roots::R # should be either ::Nothing or ::Any
    RefArray{T,A,R}(x,i,roots=nothing) where {T,A<:AbstractArray{T},R} = new(x,i,roots)
end
RefArray(x::AbstractArray{T}, i::Int, roots::Any) where {T} = RefArray{T,typeof(x),Any}(x, i, roots)
RefArray(x::AbstractArray{T}, i::Int=1, roots::Nothing=nothing) where {T} = RefArray{T,typeof(x),Nothing}(x, i, nothing)
convert(::Type{Ref{T}}, x::AbstractArray{T}) where {T} = RefArray(x, 1)

function unsafe_convert(P::Type{Ptr{T}}, b::RefArray{T}) where T
    if allocatedinline(T)
        p = pointer(b.x, b.i)
    elseif isconcretetype(T) && T.mutable
        p = pointer_from_objref(b.x[b.i])
    else
        # see comment on equivalent branch for RefValue
        p = pointerref(Ptr{Ptr{Cvoid}}(pointer(b.x, b.i)), 1, Core.sizeof(Ptr{Cvoid}))
    end
    return convert(P, p)
end
function unsafe_convert(P::Type{Ptr{Any}}, b::RefArray{Any})
    return convert(P, pointer(b.x, b.i))
end
unsafe_convert(::Type{Ptr{Cvoid}}, b::RefArray{T}) where {T} = convert(Ptr{Cvoid}, unsafe_convert(Ptr{T}, b))

###
if is_primary_base_module
    Ref(x::Any) = RefValue(x)
    Ref{T}() where {T} = RefValue{T}() # Ref{T}()
    Ref{T}(x) where {T} = RefValue{T}(x) # Ref{T}(x)

    Ref(x::Ref, i::Integer) = (i != 1 && error("Ref only has one element"); x)
    Ref(x::Ptr{T}, i::Integer) where {T} = x + (i - 1) * Core.sizeof(T)

    # convert Arrays to pointer arrays for ccall
    function Ref{P}(a::Array{<:Union{Ptr,Cwstring,Cstring}}) where P<:Union{Ptr,Cwstring,Cstring}
        return RefArray(a) # effectively a no-op
    end
    function Ref{P}(a::Array{T}) where P<:Union{Ptr,Cwstring,Cstring} where T
        if (!isbitstype(T) && T <: eltype(P))
            # this Array already has the right memory layout for the requested Ref
            return RefArray(a,1,false) # root something, so that this function is type-stable
        else
            ptrs = Vector{P}(undef, length(a)+1)
            roots = Vector{Any}(undef, length(a))
            for i = 1:length(a)
                root = cconvert(P, a[i])
                ptrs[i] = unsafe_convert(P, root)::P
                roots[i] = root
            end
            ptrs[length(a)+1] = C_NULL
            return RefArray(ptrs,1,roots)
        end
    end
    Ref(x::AbstractArray, i::Integer) = RefArray(x, i)
end

cconvert(::Type{Ptr{P}}, a::Array{<:Ptr}) where {P<:Ptr} = a
cconvert(::Type{Ref{P}}, a::Array{<:Ptr}) where {P<:Ptr} = a
cconvert(::Type{Ptr{P}}, a::Array) where {P<:Union{Ptr,Cwstring,Cstring}} = Ref{P}(a)
cconvert(::Type{Ref{P}}, a::Array) where {P<:Union{Ptr,Cwstring,Cstring}} = Ref{P}(a)

# pass NTuple{N,T} as Ptr{T}/Ref{T}
cconvert(::Type{Ref{T}}, t::NTuple{N,T}) where {N,T} = Ref{NTuple{N,T}}(t)
cconvert(::Type{Ref{T}}, r::Ref{NTuple{N,T}}) where {N,T} = r
unsafe_convert(::Type{Ref{T}}, r::Ref{NTuple{N,T}}) where {N,T} =
    convert(Ptr{T}, unsafe_convert(Ptr{NTuple{N,T}}, r))
unsafe_convert(::Type{Ptr{T}}, r::Ref{NTuple{N,T}}) where {N,T} =
    convert(Ptr{T}, unsafe_convert(Ptr{NTuple{N,T}}, r))
unsafe_convert(::Type{Ptr{T}}, r::Ptr{NTuple{N,T}}) where {N,T} =
    convert(Ptr{T}, r)

###

getindex(b::RefArray) = b.x[b.i]
setindex!(b::RefArray, x) = (b.x[b.i] = x; b)

###

"""
    LLVMPtr{T, AS}

A pointer type that more closely resembles LLVM semantics: It includes the pointer address
space, and will be passed as an actual pointer instead of an integer.

This type is mainly used to interface with code that has strict requirements about pointers,
e.g., intrinsics that are selected based on the address space, or back-ends that require
pointers to be identifiable by their types.
"""
Core.LLVMPtr