Merge pull request #30919 from JuliaLang/ptr_init

No-arg Ptr constructor.

NEWS.md

@@ -38,6 +38,7 @@ Standard library changes
 * `hasmethod` can now check for matching keyword argument names ([#30712]).
 * `startswith` and `endswith` now accept a `Regex` for the second argument ([#29790]).
 * `retry` supports arbitrary callable objects ([#30382]).
+* A no-argument construct to `Ptr{T}` has been added which constructs a null pointer ([#30919])
 
 #### LinearAlgebra
 
@@ -79,6 +80,7 @@ Deprecated or removed
 [#21598]: https://github.com/JuliaLang/julia/issues/21598
 [#24980]: https://github.com/JuliaLang/julia/issues/24980
 [#28850]: https://github.com/JuliaLang/julia/issues/28850
+[#29777]: https://github.com/JuliaLang/julia/issues/29777
 [#29790]: https://github.com/JuliaLang/julia/issues/29790
 [#29998]: https://github.com/JuliaLang/julia/issues/29998
 [#30061]: https://github.com/JuliaLang/julia/issues/30061
@@ -88,6 +90,7 @@ Deprecated or removed
 [#30349]: https://github.com/JuliaLang/julia/issues/30349
 [#30372]: https://github.com/JuliaLang/julia/issues/30372
 [#30382]: https://github.com/JuliaLang/julia/issues/30382
+[#30577]: https://github.com/JuliaLang/julia/issues/30577
 [#30583]: https://github.com/JuliaLang/julia/issues/30583
 [#30584]: https://github.com/JuliaLang/julia/issues/30584
 [#30593]: https://github.com/JuliaLang/julia/issues/30593
@@ -96,3 +99,4 @@ Deprecated or removed
 [#30712]: https://github.com/JuliaLang/julia/issues/30712
 [#30724]: https://github.com/JuliaLang/julia/issues/30724
 [#30915]: https://github.com/JuliaLang/julia/issues/30915
+[#30919]: https://github.com/JuliaLang/julia/issues/30919

base/pointer.jl

@@ -8,6 +8,13 @@ memory is actually valid, or that it actually represents data of the specified t
 """
 Ptr
 
+"""
+ Ptr{T}()
+
+Creates a null pointer to type `T`.
+"""
+Ptr{T}() where {T} = Ptr{T}(C_NULL)
+
 ## converting pointers to an appropriate unsigned ##
 
 """

test/misc.jl

@@ -730,3 +730,6 @@ end
  @test isless(b, a)
  @test sort([a, b]) == [b, a]
 end
+
+# Pointer 0-arg constructor
+@test Ptr{Cvoid}() == C_NULL