Merge pull request #83 from JuliaAlgebra/bl/fix82

Defines oneunit for AbstractVariable

Author: blegat

src/monomial.jl

@@ -124,3 +124,11 @@ mapexponents(f, m1::AbstractMonomialLike, m2::AbstractMonomialLike) = mapexponen
 
 Base.one(::Type{TT}) where {TT<:AbstractMonomialLike} = constantmonomial(TT)
 Base.one(t::AbstractMonomialLike) = constantmonomial(t)
+# See https://github.com/JuliaAlgebra/MultivariatePolynomials.jl/issues/82
+# By default, Base do oneunit(v::VT) = VT(one(v)).
+# This tries to convert a monomial to a variable which does not work.
+# The issue here is there is no way to represent the multiplicative identity
+# using the variable type. The best we can do is return a monomial even
+# if it does not exactly match the definition of oneunit.
+Base.oneunit(v::AbstractVariable) = one(v)
+Base.oneunit(VT::Type{<: AbstractVariable}) = one(VT)

test/variable.jl

@@ -20,9 +20,6 @@ import MultivariatePolynomials: AbstractVariable, similarvariable, @similarvaria
         @test iszero(zero(x))
         @test zero(x) isa AbstractPolynomial{Int}
         @inferred zero(x)
-        @test one(x) == 1
-        @test one(x) isa AbstractMonomial
-        @inferred one(x)
 
         typetests(x)
         @test (@inferred polynomial(x)) isa AbstractPolynomial{Int}
@@ -40,6 +37,18 @@ import MultivariatePolynomials: AbstractVariable, similarvariable, @similarvaria
 
         @test divides(x, x) == true
         @test divides(x, y) == false
+
+        @testset "Issue #82" begin
+            for v in (x, typeof(x))
+                for fun in (oneunit, one)
+                    @test fun(v) == 1
+                    @test 1 == fun(v)
+                    #@test isone(fun(v)) # Enable when Julia v0.6 is dropped
+                    @test fun(v) isa AbstractMonomial
+                    @inferred fun(v)
+                end
+            end
+        end
     end
     @testset "Create similar variable" begin
         Mod.@polyvar x y