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decrease method count for eltype for Tuple, decrease max_methods #58788

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decrease method count for eltype for Tuple, decrease max_methods #58788

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2e32141
decrease method count for `eltype` for `Tuple`, decrease `max_methods`
nsajko Jun 21, 2025
aeb3a5d
Merge branch 'master' into decrease_method_count_for_eltype_Tuple_to_…
nsajko Jun 27, 2025
ffe4496
Merge branch 'master' into decrease_method_count_for_eltype_Tuple_to_…
nsajko Jul 2, 2025
afa2383
Merge branch 'master' into decrease_method_count_for_eltype_Tuple_to_…
nsajko Jul 7, 2025
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29 changes: 11 additions & 18 deletions base/tuple.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -269,10 +269,18 @@ first(t::Tuple) = t[1]

# eltype

eltype(::Type{Tuple{}}) = Bottom
# the <: here makes the runtime a bit more complicated (needing to check isdefined), but really helps inference
eltype(t::Type{<:Tuple{Vararg{E}}}) where {E} = @isdefined(E) ? (E isa Type ? E : Union{}) : _compute_eltype(t)
eltype(t::Type{<:Tuple}) = _compute_eltype(t)
_eltype_ntuple(t::Type{<:Tuple{Vararg{E}}}) where {E} = @isdefined(E) ? (E isa Type ? E : Union{}) : _compute_eltype(t)
# We'd like to be able to infer eltype(::Tuple), so keep the number of eltype(::Type{<:Tuple}) methods at max_methods!
function eltype(t::Type{<:Tuple})
if t <: Tuple{}
Bottom
elseif t <: NTuple
_eltype_ntuple(t)
else
_compute_eltype(t)
end
end
function _compute_eltype(@nospecialize t)
@_total_meta
has_free_typevars(t) && return Any
Expand All @@ -297,21 +305,6 @@ function _compute_eltype(@nospecialize t)
return r
end

# We'd like to be able to infer eltype(::Tuple), which needs to be able to
# look at these four methods:
#
# julia> methods(Base.eltype, Tuple{Type{<:Tuple}})
# 4 methods for generic function "eltype" from Base:
# [1] eltype(::Type{Union{}})
# @ abstractarray.jl:234
# [2] eltype(::Type{Tuple{}})
# @ tuple.jl:199
# [3] eltype(t::Type{<:Tuple{Vararg{E}}}) where E
# @ tuple.jl:200
# [4] eltype(t::Type{<:Tuple})
# @ tuple.jl:209
typeof(function eltype end).name.max_methods = UInt8(4)

# key/val types
keytype(@nospecialize t::Tuple) = keytype(typeof(t))
keytype(@nospecialize T::Type{<:Tuple}) = Int
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2 changes: 1 addition & 1 deletion test/ambiguous.jl
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Expand Up @@ -349,7 +349,7 @@ end
let need_to_handle_undef_sparam =
Set{Method}(detect_unbound_args(Base; recursive=true, allowed_undefineds))
pop!(need_to_handle_undef_sparam, which(Base._totuple, (Type{Tuple{Vararg{E}}} where E, Any, Any)))
pop!(need_to_handle_undef_sparam, which(Base.eltype, Tuple{Type{Tuple{Any}}}))
pop!(need_to_handle_undef_sparam, which(Base._eltype_ntuple, Tuple{Type{Tuple{Any}}}))
pop!(need_to_handle_undef_sparam, first(methods(Base.same_names)))
@test_broken isempty(need_to_handle_undef_sparam)
pop!(need_to_handle_undef_sparam, which(Base._cat, Tuple{Any, AbstractArray}))
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