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Merged
blegat merged 1 commit into from
Apr 7, 2026
Merged

Ensure monomial_type is constant-folded #103

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6 changes: 5 additions & 1 deletion src/promotion.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -56,6 +56,10 @@ function MP.monomial_type(vars::Tuple{V,Vararg{Variable}}) where {V<:Variable}
return Monomial{sorted, length(sorted)}
end

_instantiate(::Type{Tuple{}}) = ()
_instantiate(::Type{T}) where {T<:Tuple} =
(Base.tuple_type_head(T)(), _instantiate(Base.tuple_type_tail(T))...)

function MP.monomial_type(::Type{T}) where {T<:Tuple{Variable,Vararg{Variable}}}
return monomial_type(tuple((V() for V in fieldtypes(T))...))
return monomial_type(_instantiate(T))
end
6 changes: 6 additions & 0 deletions test/promotion.jl
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Expand Up @@ -56,6 +56,12 @@ end
@test @inferred(monomial_type(typeof((x,)))) == Monomial{(x,), 1}
@test @inferred(monomial_type(typeof((x, y)))) == Monomial{(x, y), 2}
@test @inferred(monomial_type(typeof((x, y, z)))) == Monomial{(x, y, z), 3}

# Test that `monomial_type` on Tuple types is constant-folded,
# so that branches on it are eliminated at compile time.
_mt_branch(::Type{V}) where {V} =
monomial_type(V) === Monomial{(x, y), 2} ? Int : String
@test @inferred(_mt_branch(typeof((x, y)))) === Int
end

@testset "conversion" begin
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