add mode traits for convert

src/GeoFormatTypes.jl

@@ -9,19 +9,23 @@ end GeoFormatTypes
 
 export GeoFormat
 
-export CoordinateReferenceSystemFormat, EPSG, ProjString 
+export CoordinateReferenceSystemFormat, EPSG, ProjString, CoordSys
 
 export GeometryFormat, GeoJSON, KML
 
-export MixedFormat, GML 
+export MixedFormat, GML
 
 export AbstractWellKnownText, WellKnownText, WellKnownText2, ESRIWellKnownText, WellKnownBinary
 
 const PROJ_PREFIX = "+proj="
 const EPSG_PREFIX = "EPSG:"
 # TODO more verification that types are wrapping the right format.
 
-
+# Traits for mixed crs/geometry formats.
+abstract type FormatMode end
+struct Geom <: FormatMode end
+struct CRS <: FormatMode end
+struct Mixed <: FormatMode end
 
 """
     val(f::GeoFormat)
@@ -35,6 +39,25 @@ Abstract supertype for geospatial data formats
 """
 abstract type GeoFormat end
 
+# Convert from the same type does nothing.
+Base.convert(::T, source::S) where {T<:GeoFormat,S<:T} = source
+# Convert uses the `mode` trait to distinguish crs form geometry conversion
+Base.convert(target::Type{<:GeoFormat}, input::GeoFormat) = begin
+    inputmode = mode(input)
+    targetmode = mode(target)
+    if inputmode isa Mixed
+        if targetmode isa Mixed
+            throw(ArgumentError("convert mode cannot be determined: please specify CRS() or Geom for mode in convert(::T, mode, source)"))
+        else
+            convert(target, targetmode, input)
+        end
+    elseif targetmode isa typeof(inputmode)
+        convert(target, inputmode, input)
+    else
+        throw(ArgumentError("cannot convert $(typeof(input)) to $target"))
+    end
+end
+
 """
 Formats representing coordinate reference systems
 """
@@ -49,10 +72,16 @@ abstract type GeometryFormat <: GeoFormat end
 """
 Formats that may hold either or both coordinate reference systems and geometries.
 """
-abstract type MixedFormat <: GeoFormat end
+abstract type MixedFormat{X} <: GeoFormat end
 
 val(x::GeoFormat) = x.val
 
+mode(format::GeoFormat) = mode(typeof(format))
+mode(::Type{<:GeometryFormat}) = Geom()
+mode(::Type{<:CoordinateReferenceSystemFormat}) = CRS()
+mode(::Type{<:MixedFormat}) = Mixed()
+mode(::Type{<:MixedFormat{M}}) where M = M()
+
 # Most GeoFormat types wrap String or have a constructor for string inputs
 Base.convert(::Type{String}, input::GeoFormat) = val(input)
 Base.convert(::Type{T}, input::AbstractString) where T <: GeoFormat = T(input)
@@ -70,44 +99,56 @@ struct ProjString <: CoordinateReferenceSystemFormat
 end
 
 """
-Well known text has a number of versions and standards, and can 
+Mapinfo CoordSys string
+"""
+struct CoordSys <: CoordinateReferenceSystemFormat
+    val::String
+end
+
+"""
+Well known text has a number of versions and standards, and can
 represent coordinate reference systems or geometric data.
 """
-abstract type AbstractWellKnownText <: MixedFormat end
+abstract type AbstractWellKnownText{X} <: MixedFormat{X} end
 
 """
 Well known text v1 following the OGC standard
 """
-struct WellKnownText <: AbstractWellKnownText
-    val::String
+struct WellKnownText{X,T<:String} <: AbstractWellKnownText{X}
+    mode::X
+    val::T
 end
 
 """
 Well known text v2 following the new OGC standard
 """
-struct WellKnownText2 <: AbstractWellKnownText
-    val::String
+struct WellKnownText2{X,T<:String} <: AbstractWellKnownText{X}
+    mode::X
+    val::T
 end
 
 """
 Well known text following the ESRI standard
 """
-struct ESRIWellKnownText <: AbstractWellKnownText
-    val::String
+struct ESRIWellKnownText{X,T<:String} <: AbstractWellKnownText{X}
+    mode::X
+    val::T
 end
 
 """
 Well known binary
 """
-struct WellKnownBinary{T} <: AbstractWellKnownText
+struct WellKnownBinary{X,T} <: MixedFormat{X}
+    mode::X
     val::T
 end
 
-Base.convert(::Type{String}, input::WellKnownBinary) = error("`convert` is not defined for `WellKnownBinary`")
+Base.convert(::Type{String}, input::WellKnownBinary) =
+    error("`convert` to `String` is not defined for `WellKnownBinary`")
 
 
 """
-EPSG code representing a coordinate reference system from the 
+EPSG code representing a coordinate reference system from the
 EPSG spatial reference system registry.
 """
 struct EPSG <: CoordinateReferenceSystemFormat
@@ -137,8 +178,9 @@ end
 """
 Geography Markup Language
 """
-struct GML <: MixedFormat
-    val::String
+struct GML{X,T<:String} <: MixedFormat{X}
+    mode::X
+    val::T
 end
 
 """

test/runtests.jl

@@ -1,4 +1,5 @@
 using GeoFormatTypes, Test
+using GeoFormatTypes: Geom, CRS, Mixed
 
 @test_throws ArgumentError ProjString("+lat_ts=56.5 +ellps=GRS80")
 convert(String, ProjString("+proj=merc +lat_ts=56.5 +ellps=GRS80")) == "+proj=merc +lat_ts=56.5 +ellps=GRS80"
@@ -8,9 +9,11 @@ convert(String, ProjString("+proj=merc +lat_ts=56.5 +ellps=GRS80")) == "+proj=me
 @test convert(String, EPSG(4326)) == "EPSG:4326" 
 @test convert(Int, EPSG("EPSG:4326")) == 4326 
 
-@test convert(String, WellKnownText("test")) == "test"
-@test convert(String, WellKnownText2("test")) == "test"
-@test convert(String, ESRIWellKnownText("test")) == "test"
-@test convert(String, GML("test")) == "test"
+@test convert(String, WellKnownText(Geom(), "test")) == "test"
+@test convert(String, WellKnownText2(CRS(), "test")) == "test"
+@test convert(String, ESRIWellKnownText(Geom(), "test")) == "test"
+@test convert(String, GML(Mixed(), "test")) == "test"
 @test convert(String, KML("test")) == "test"
 @test convert(String, GeoJSON("test")) == "test"
+
+@test_throws ArgumentError convert(KML, ProjString("+proj=test"))