Implement eltype for list

src/PersistentList.jl

@@ -43,6 +43,11 @@ Base.isequal(l1::PersistentList, l2::PersistentList) =
 ==(l1::PersistentList, l2::PersistentList) =
     head(l1) == head(l2) && tail(l1) == tail(l2)
 
+Base.eltype(::Type{<:AbstractList{T}}) where {T} = T
+Base.IteratorEltype(::Type{<:AbstractList{T}}) where {T} = Base.HasEltype()
+Base.IteratorSize(::Type{<:EmptyList}) = Base.HasLength()
+Base.IteratorSize(::Type{<:PersistentList}) = Base.HasLength()
+
 Base.iterate(l::AbstractList) = iterate(l, l)
 Base.iterate(::AbstractList, ::EmptyList) = nothing
 Base.iterate(::AbstractList, l::PersistentList) = (head(l), tail(l))

test/PersistentListTest.jl

@@ -2,6 +2,22 @@ using FunctionalCollections
 using Test
 
 @testset "Persistent Lists" begin
+    @testset "iterator interface" begin
+        l1 = plist([1,2,3])
+        l2 = plist(Int[])
+        T1 = typeof(l1)
+        T2 = typeof(l2)
+
+        @test Base.IteratorSize(T1) == Base.HasLength()
+        @test Base.IteratorSize(T2) == Base.HasLength()
+        @test Base.IteratorEltype(T1) == Base.HasEltype()
+        @test Base.IteratorEltype(T2) == Base.HasEltype()
+        @test Base.eltype(T1) == Int
+        @test Base.eltype(T2) == Int
+
+        @test Base.eltype(typeof(collect(l1))) == Int
+        @test Base.eltype(typeof(collect(l2))) == Int
+    end
 
     @testset "length" begin
         @test length(PersistentList([1])) == 1