fixup! allow undefined initial_value

Author: vchuravy

base/scopedvalues.jl

@@ -38,13 +38,15 @@ julia> sval[]
     implementation is available from the package ScopedValues.jl.
 """
 mutable struct ScopedValue{T}
-    const initial_value::T
-    ScopedValue{T}() where T = new()
-    ScopedValue{T}(val) where T = new{T}(val)
-    ScopedValue(val::T) where T = new{T}(val)
+    const has_default::Bool
+    const default::T
+    ScopedValue{T}() where T = new(false)
+    ScopedValue{T}(val) where T = new{T}(true, val)
+    ScopedValue(val::T) where T = new{T}(true, val)
 end
 
 Base.eltype(::ScopedValue{T}) where {T} = T
+Base.isassigned(val::ScopedValue) = val.has_default
 
 const ScopeStorage = Base.PersistentDict{ScopedValue, Any}
 
@@ -99,12 +101,12 @@ function get(val::ScopedValue{T}) where {T}
     # Inline current_scope to avoid doing the type assertion twice.
     scope = current_task().scope
     if scope === nothing
-        isdefined(val, :initial_value) && return Some(val.initial_value)
+        isassigned(val) && return Some(val.default)
         return nothing
     end
     scope = scope::Scope
-    if isdefined(val, :initial_value)
-        return Some(Base.get(scope.values, val, val.initial_value)::T)
+    if isassigned(val)
+        return Some(Base.get(scope.values, val, val.default)::T)
     else
         v = Base.get(scope.values, val, novalue)
         v === novalue || return Some(v::T)
@@ -124,7 +126,7 @@ function Base.show(io::IO, val::ScopedValue)
     print(io, '(')
     v = get(val)
     if v === nothing
-        print(io, "(undefined)")
+        print(io, "undefined")
     else
         show(IOContext(io, :typeinfo => eltype(val)), something(v))
     end

test/scopedvalues.jl

@@ -4,12 +4,13 @@ import Base: ScopedValues
 @testset "errors" begin
     @test ScopedValue{Float64}(1)[] == 1.0
     @test_throws InexactError ScopedValue{Int}(1.5)
-    var = ScopedValue(1)
-    @test_throws MethodError var[] = 2
+    val = ScopedValue(1)
+    @test_throws MethodError val[] = 2
     with() do
-        @test_throws MethodError var[] = 2
+        @test_throws MethodError val[] = 2
     end
-    @test_throws MethodError ScopedValue{Int}()
+    val = ScopedValue{Int}()
+    @test_throws KeyError val[]
     @test_throws MethodError ScopedValue()
 end
 
@@ -61,6 +62,7 @@ import Base.Threads: @spawn
 end
 
 @testset "show" begin
+    @test sprint(show, ScopedValue{Int}()) == "ScopedValue{$Int}(undefined)"
     @test sprint(show, sval) == "ScopedValue{$Int}(1)"
     @test sprint(show, ScopedValues.current_scope()) == "nothing"
     with(sval => 2.0) do