Add corresponding operate_to! method for Matrix-scalar product (#273)

src/dispatch.jl

@@ -468,10 +468,35 @@ end
 # +(::SparseMatrixCSC) is not defined for generic types in Base.
 Base.:+(A::AbstractArray{<:AbstractMutable}) = A
 
+# `Base.*(::AbstractArray, α)` is only defined if `α isa Number`
+# Currently, mutable types are scalar elements (e.g. JuMP expression,
+# MOI functions or polynomials) so broadcasting is the right dispatch.
+# If this causes issues in the future, e.g., because a user define a non-scalar
+# subtype of `AbstractMutable`, we might want to check that
+# `ndims` is zero and error otherwise.
+
 Base.:*(α::AbstractMutable, A::AbstractArray) = α .* A
 
 Base.:*(A::AbstractArray, α::AbstractMutable) = A .* α
 
+function operate_to!(
+    output::AbstractArray,
+    ::typeof(*),
+    v::AbstractArray,
+    α::Union{Number,AbstractMutable},
+)
+    return Base.broadcast!(*, output, v, α)
+end
+
+function operate_to!(
+    output::AbstractArray,
+    ::typeof(*),
+    α::Union{Number,AbstractMutable},
+    v::AbstractArray,
+)
+    return Base.broadcast!(*, output, α, v)
+end
+
 # Needed for Julia v1.0, otherwise, `broadcast(*, α, A)` gives a `Array` and
 # not a `Symmetric`.
 

test/dispatch.jl

@@ -85,3 +85,24 @@ end
     @test 2im * B == C
     @test C isa Matrix{Complex{BigInt}}
 end
+
+@testset "operate_to!(::Array, ::typeof(*), ::AbstractMutable, ::Array)" begin
+    for A in ([1 2; 5 3], DummyBigInt[1 2; 5 3])
+        for x in (2, DummyBigInt(2))
+            # operate_to!(::Array, *, ::AbstractMutable, ::Array)
+            B = x * A
+            C = zero(B)
+            D = MA.operate_to!(C, *, x, A)
+            @test C === D
+            @test typeof(B) == typeof(C)
+            @test MA.isequal_canonical(B, C)
+            # operate_to!(::Array, *, ::Array, ::AbstractMutable)
+            B = A * x
+            C = zero(B)
+            D = MA.operate_to!(C, *, A, x)
+            @test C === D
+            @test typeof(B) == typeof(C)
+            @test MA.isequal_canonical(B, C)
+        end
+    end
+end