improve inferrability of seek(::Stateful, sentinel) (#38625)

the current inference can't propagate constant values or `isa` condition of object fields, and this helps inference eliminate the possibility of `getindex(s.nextvalstate::Nothing, 1)` call
JuliaLang · Nov 30, 2020 · 8ea6365 · 8ea6365 · nanosoldier · Dec 1, 2020
1 parent bc0b9a7
commit 8ea6365
Showing 1 changed file with 4 additions and 1 deletion.
diff --git a/base/iterators.jl b/base/iterators.jl
@@ -1296,7 +1296,10 @@ convert(::Type{Stateful}, itr) = Stateful(itr)
  end
 end
 
-@inline peek(s::Stateful, sentinel=nothing) = s.nextvalstate !== nothing ? s.nextvalstate[1] : sentinel
+@inline function peek(s::Stateful, sentinel=nothing)
+ ns = s.nextvalstate
+ return ns !== nothing ? ns[1] : sentinel
+end
 @inline iterate(s::Stateful, state=nothing) = s.nextvalstate === nothing ? nothing : (popfirst!(s), nothing)
 IteratorSize(::Type{Stateful{T,VS}}) where {T,VS} = IteratorSize(T) isa HasShape ? HasLength() : IteratorSize(T)
 eltype(::Type{Stateful{T, VS}} where VS) where {T} = eltype(T)