first pass get/set queries

src/optics.jl

@@ -346,3 +346,92 @@ end
 Base.@propagate_inbounds function set(obj, lens::DynamicIndexLens, val)
     return setindex(obj, val, lens.f(obj)...)
 end
+
+abstract type AbstractQuery end
+
+struct Query{F1,F2} <: AbstractQuery
+    select::F1
+    ignore::F2
+end
+Query(select) = Query(select, x -> false)
+Query(; select, ignore=x -> false) = Query(select, ignore)
+
+queryargs(::Query, obj, fn, val) = (val,)
+
+struct ParentQuery{F1,F2} <: AbstractQuery
+    select::F1
+    ignore::F2
+end
+ParentQuery(select) = ParentQuery(select, x -> false)
+ParentQuery(; select, ignore=x -> false) = ParentQuery(select, ignore)
+
+queryargs(::ParentQuery, obj, fn, val) = (obj, fn)
+
+@inline (optic::AbstractQuery)(obj) = _getall(obj, optic)
+@inline set(obj, optic::AbstractQuery, xs) = first(first(_setall(obj, optic, xs)))
+
+struct Changed end
+struct Unchanged end
+
+@inline function modify(f, obj, optic::AbstractQuery)
+    set(obj, optic, map(f, optic(obj)))
+end
+
+@generated function _getall(obj::O, optic::AbstractQuery) where O
+    exp = Expr(:tuple)
+    for fieldname in fieldnames(O)
+        v = quote
+            fn = $(QuoteNode(fieldname))
+            val = getfield(obj, fn)
+            args = queryargs(optic, obj, fn, val)
+            if optic.select(args...)
+                (val,)
+            elseif !optic.ignore(args...)
+                _getall(val, optic)
+            else
+                ()
+            end
+        end
+        # Splat the result into the output tuple
+        push!(exp.args, Expr(:..., v))
+    end
+    exp
+end
+
+@generated function _setall(obj::O, optic::AbstractQuery, xs, n=1) where O
+    exp = Expr(:tuple)
+    for fieldname in fieldnames(O)
+         v = quote
+            fn = $(QuoteNode(fieldname))
+            val = getfield(obj, fn)
+            args = queryargs(optic, obj, fn, val)
+            if optic.select(args...)
+                pair = xs[n] => Changed()
+                n += 1
+                pair
+            elseif !optic.ignore(args...)
+                pair, n = _setall(val, optic, xs, n)
+                pair
+            else
+                val => Unchanged()
+            end
+        end
+        push!(exp.args, v)
+    end
+    quote
+        pairs = $exp
+        vals = map(first, pairs)
+        changes = map(last, pairs)
+        _maybeconstruct(obj, vals, changes), n
+    end
+end
+
+@generated function _maybeconstruct(obj, vals, changes::C) where C 
+    if Changed in fieldtypes(C)
+        :(_maybeconstruct(Changed(), obj, vals))
+    else
+        :(_maybeconstruct(Unchanged(), obj, vals))
+    end
+end
+_maybeconstruct(::Changed, obj::O, vals) where O = constructorof(O)(vals...) => Changed()
+_maybeconstruct(::Unchanged, obj, vals) = obj => Unchanged()

test/test_optics.jl

@@ -5,7 +5,8 @@ using Test
 
 @testset "Properties" begin
     pt = (x=1, y=2, z=3)
-    @test (x=0, y=1, z=2) === @set pt |> Properties() -= 1
+    @test (x=0, y=1, z=2) === 
+    @set pt |> Properties(pt) -= 1
 end
 
 @testset "Elements" begin

test/test_queries.jl

@@ -0,0 +1,20 @@
+using Accessors, ConstructionBase, BenchmarkTools
+
+optic = Accessors.Query(x -> x isa Int)
+obj = (7, (a=17.0, b=2.0f0), ("3", 4, 5))
+vals = (1.0, 2.0, 3.0, 4.0)
+
+@btime $optic($obj)
+@btime set($obj, $optic, $vals)
+# Compiles away
+@btime modify(x -> 2x, $vals, $optic)
+
+
+unstable_optic = Accessors.Query(x -> x isa Number && x > 2)
+
+# This is slow
+@btime set($x, $unstable_optic, $y)
+
+# This still compiles away
+@btime modify(x -> 2x, $vals, $unstable_optic)
+