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Merged
merged 2 commits into from
Jan 1, 2023
Merged

stop using Base.convert #66

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f329ce5
stop using Base.convert
visr Aug 3, 2022
32df099
move convert no-op to interface.jl
visr Aug 4, 2022
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10 changes: 6 additions & 4 deletions docs/src/guides/developer.md
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Expand Up @@ -42,12 +42,14 @@ And lastly, there are many other optional functions for each specific geometry.
### Conversion
It is useful if others can convert any custom geometry into your
geometry type, if their custom geometry supports GeoInterface as well.
This requires the following three methods, and the last one requires more code to generate `T` with `ngeom`, `getgeom` or just `coordinates` calls.
This requires the following methods, where the implementation should be defined in terms
of GeoInterface methods like `ngeom`, `getgeom`, or just `coordinates` calls.

```julia
Base.convert(::Type{T}, geom) where T<:AbstractPackageType = Base.convert(T, geomtrait(geom), geom)
Base.convert(::Type{T}, ::LineStringTrait, geom::T) = geom # fast fallthrough without conversion
Base.convert(::Type{T}, ::LineStringTrait, geom) = ... # slow custom conversion based on ngeom and getgeom
# This method will get called on GeoInterface.convert(::Type{T}, geom)
# if geomtrait(geom) == LineStringTrait()
GeoInterface.convert(::Type{CustomLineString}, ::LineStringTrait, geom) = ...
GeoInterface.convert(::Type{CustomPolygon}, ::PolygonTrait, geom) = ...
```

## Required for Feature(Collection)s
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4 changes: 1 addition & 3 deletions src/fallbacks.jl
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Expand Up @@ -103,14 +103,12 @@ getfeature(t::AbstractFeatureCollectionTrait, fc) = (getfeature(t, fc, i) for i
# Backwards compatibility
coordinates(t::AbstractPointTrait, geom) = collect(getcoord(t, geom))
coordinates(t::AbstractGeometryTrait, geom) = collect(coordinates.(getgeom(t, geom)))
function coordinates(t::AbstractFeatureTrait, feature)
function coordinates(t::AbstractFeatureTrait, feature)
geom = geometry(feature)
isnothing(geom) ? [] : coordinates(geom)
end
coordinates(t::AbstractFeatureCollectionTrait, fc) = [coordinates(f) for f in getfeature(fc)]

Base.convert(T::Type, ::AbstractGeometryTrait, geom) = error("Conversion is enabled for type $T, but not implemented. Please report this issue to the package maintainer.")
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@fingolfin fingolfin Dec 31, 2022

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This method is weird, but not actually a performance problem because the Julia compiler will never insert invocations to a three-argument Base.convert method


# Subtraits

"""
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4 changes: 2 additions & 2 deletions src/interface.jl
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Expand Up @@ -606,10 +606,10 @@ coordinates(obj) = coordinates(trait(obj), obj)
"""
convert(type::CustomGeom, geom)

Convert `geom` into the `CustomGeom` type if both geom as the CustomGeom package
have implemented GeoInterface.
Create a `CustomGeom` from any `geom` that implements the GeoInterface.
"""
convert(T, geom) = convert(T, geomtrait(geom), geom)
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@fingolfin fingolfin Dec 31, 2022

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If this was changed to Base.convert, it would be highly problematic -- but not just because of potential ambiguities this introduces, but also because it would invalidate basically every method in the system, forcing Julia to recompile tons of stuff. So basically after using GeoInterface everything would have the "first time invocation overhead" again. That'd be really bad, esp. now that Julia 1.9 or 1.10 will add native code caching (i.e. generated machine code will be cached as part of precompilation -- speeding up TTFX quite a bit -- unless packages kill the benefit by invalidating methods...).

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@rafaqz rafaqz Dec 31, 2022

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Noone suggested that you may misunderstand this PR.

If we invalidate anything with convert it would be with type pyracy, which is much higher up the list of "things not to do".

But we are all on board with using the package convert it's just what to do with the fact that we already have implementations of Base.convert in the wild.

convert(::Type{T}, x::T) where {T} = x # no-op

"""
astext(geom) -> WKT
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12 changes: 2 additions & 10 deletions test/test_primitives.jl
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Expand Up @@ -35,8 +35,6 @@ using Test
GeoInterface.geomtrait(::MyCurve) = LineStringTrait()
GeoInterface.ngeom(::LineStringTrait, geom::MyCurve) = 2
GeoInterface.getgeom(::LineStringTrait, geom::MyCurve, i) = MyPoint()
Base.convert(T::Type{MyCurve}, geom::X) where {X} = Base.convert(T, geomtrait(geom), geom)
Base.convert(::Type{MyCurve}, ::LineStringTrait, geom::MyCurve) = geom

GeoInterface.isgeometry(::MyPolygon) = true
GeoInterface.geomtrait(::MyPolygon) = PolygonTrait()
Expand Down Expand Up @@ -235,15 +233,9 @@ end
struct XCurve end
struct XPolygon end

Base.convert(T::Type{XCurve}, geom::X) where {X} = Base.convert(T, geomtrait(geom), geom)
Base.convert(::Type{XCurve}, ::LineStringTrait, geom::XCurve) = geom # fast fallthrough
Base.convert(::Type{XCurve}, ::LineStringTrait, geom) = geom

geom = MyCurve()
@test !isnothing(convert(MyCurve, geom))

Base.convert(T::Type{XPolygon}, geom::X) where {X} = Base.convert(T, geomtrait(geom), geom)
@test_throws Exception convert(MyPolygon, geom)
@test GeoInterface.convert(MyCurve, geom) === geom
@test_throws Exception GeoInterface.convert(MyPolygon, geom)
end

@testset "Operations" begin
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