Condense constantspace maxspace (#451)

* condense constantspace maxspace

* preserve rangetype

Author: jishnub

src/Space.jl

@@ -649,10 +649,7 @@ end
 # domainscompatible check.
 for OP in (:maxspace,:(union))
     @eval begin
-        $OP(A::ConstantSpace{AnyDomain},B::ConstantSpace{AnyDomain}) = A
-        $OP(A::ConstantSpace{AnyDomain},B::ConstantSpace) = B
-        $OP(A::ConstantSpace,B::ConstantSpace{AnyDomain}) = A
-        $OP(A::ConstantSpace,B::ConstantSpace) = ConstantSpace(domain(A) ∪ domain(B))
+        $OP(A::ConstantSpace{<:Any,R1}, B::ConstantSpace{<:Any,R2}) where {R1,R2} = ConstantSpace(promote_type(R1,R2), domain(A) ∪ domain(B))
     end
 end
 

test/SpacesTest.jl

@@ -1,6 +1,6 @@
 using ApproxFunBase
 using Test
-using ApproxFunBase: PointSpace, HeavisideSpace, PiecewiseSegment, dimension, SVector, checkpoints
+using ApproxFunBase: PointSpace, HeavisideSpace, PiecewiseSegment, dimension, SVector, checkpoints, AnyDomain
 using StaticArrays
 using BandedMatrices: rowrange, colrange, BandedMatrix
 using LinearAlgebra
@@ -303,6 +303,11 @@ using LinearAlgebra
         @test g > f
         @test g >= f
         @test 1 < f < 3
+
+        @test maxspace(ConstantSpace(Point(1)), ConstantSpace(Point(2))) == ConstantSpace(Point(1) ∪ Point(2))
+        @test maxspace(ConstantSpace(Point(1)), ConstantSpace(AnyDomain())) == ConstantSpace(Point(1))
+        @test maxspace(ConstantSpace(AnyDomain()), ConstantSpace(Point(2))) == ConstantSpace(Point(2))
+        @test maxspace(ConstantSpace(AnyDomain()), ConstantSpace(AnyDomain())) == ConstantSpace(AnyDomain())
     end
 
     @testset "promotion" begin