Support isassigned(::RefValue) (#345)

README.md

@@ -157,6 +157,8 @@ Currently, the `@compat` macro supports the following syntaxes:
 
 * `convert` can convert between different `Set` types on 0.5 and below. ([#18727])
 
+* `isassigned(::RefValue)` is supported on 0.5 and below. ([#18082])
+
 * `unsafe_trunc(::Type{<:Integer}, ::Integer)` is supported on 0.5. ([#18629])
 
 ## Renamed functions
@@ -335,6 +337,7 @@ includes this fix. Find the minimum version from there.
 [#17323]: https://github.com/JuliaLang/julia/issues/17323
 [#17510]: https://github.com/JuliaLang/julia/issues/17510
 [#17623]: https://github.com/JuliaLang/julia/issues/17623
+[#18086]: https://github.com/JuliaLang/julia/issues/18086
 [#18380]: https://github.com/JuliaLang/julia/issues/18380
 [#18484]: https://github.com/JuliaLang/julia/issues/18484
 [#18510]: https://github.com/JuliaLang/julia/issues/18510

src/Compat.jl

@@ -1450,6 +1450,11 @@ if VERSION < v"0.6.0-dev.838"
     Base.convert{T}(::Type{Set{T}}, s::Set) = Set{T}(s)
 end
 
+# https://github.com/JuliaLang/julia/pull/18082
+if VERSION < v"0.6.0-dev.2347"
+    Base.isassigned(x::Base.RefValue) = isdefined(x, :x)
+end
+
 if VERSION < v"0.6.0-dev.735"
     Base.unsafe_trunc{T<:Integer}(::Type{T}, x::Integer) = rem(x, T)
 end

test/runtests.jl

@@ -1805,6 +1805,10 @@ let
     @test cssset == Set(["foo", "bar"])
 end
 
+# PR 18082
+@test !isassigned(Ref{String}())
+@test isassigned(Ref{String}("Test"))
+
 @test unsafe_trunc(Int8, 128) === Int8(-128)
 @test_throws InexactError trunc(Int8, 128)