add poly promotion for MultiPolygon

src/basic_types.jl

@@ -321,6 +321,17 @@ function coordinates(polygon::Polygon{N,T}) where {N,T}
     end
 end
 
+function Base.promote_rule(::Type{Polygon{N, T1}}, ::Type{Polygon{N, T2}}) where {N, T1, T2}
+    return Polygon{N, promote_rule(T1, T2)}
+end
+
+function Base.convert(::Type{Polygon{N, T}}, poly::Polygon{N}) where {N, T}
+    return Polygon(
+        convert(Vector{Point{N, T}}, poly.exterior),
+        convert(Vector{Vector{Point{N, T}}}, poly.interiors),
+    )
+end
+
 """
     MultiPolygon(polygons::AbstractPolygon)
 
@@ -333,6 +344,10 @@ end
 function MultiPolygon(polygons::AbstractVector{<:AbstractPolygon{Dim,T}}) where {Dim,T}
     return MultiPolygon(convert(Vector{eltype(polygons)}, polygons))
 end
+function MultiPolygon(polygons::AbstractVector{<:AbstractPolygon{Dim}}) where {Dim}
+    T = reduce(promote_type, typeof.(polygons), init = eltype(polygons))
+    return MultiPolygon(convert(Vector{T}, polygons))
+end
 
 Base.getindex(mp::MultiPolygon, i) = mp.polygons[i]
 Base.size(mp::MultiPolygon) = size(mp.polygons)

test/polygons.jl

@@ -15,15 +15,16 @@
         p2 = Polygon(OffsetArray(exterior, 0), interiors)
         @test p2 == p1
 
-        # TODO: promote polygon type automatically when creating MultiPolygon
-        polygon = Polygon(Point2f.(points))
+        polygon = Polygon(points)
         mp = MultiPolygon([polygon, p1, p2])
         @test mp.polygons == [polygon, p1, p2]
         @test mp[1] == polygon
         @test mp[2] == p1
         @test size(mp) == (3,) # TODO: What does size even mean here?
         @test length(mp) == 3
         @test MultiPolygon(OffsetArray([polygon, p1, p2], 0)) == mp
+        mp = MultiPolygon([Polygon(Point2f.()), p1, p2])
+
     end
 
     rect = Rect2f(0, 0, 1, 1)