diff --git a/Project.toml b/Project.toml
index cd9cc86d..e90d3ac1 100644
--- a/Project.toml
+++ b/Project.toml
@@ -15,16 +15,22 @@ Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 
 [weakdeps]
 AxisKeys = "94b1ba4f-4ee9-5380-92f1-94cde586c3c5"
+Dates = "ade2ca70-3891-5945-98fb-dc099432e06a"
 IntervalSets = "8197267c-284f-5f27-9208-e0e47529a953"
+LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
 Requires = "ae029012-a4dd-5104-9daa-d747884805df"
 StaticArrays = "90137ffa-7385-5640-81b9-e52037218182"
 StructArrays = "09ab397b-f2b6-538f-b94a-2f83cf4a842a"
+Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 
 [extensions]
 AccessorsAxisKeysExt = "AxisKeys"
+AccessorsDatesExt = "Dates"
 AccessorsIntervalSetsExt = "IntervalSets"
+AccessorsLinearAlgebraExt = "LinearAlgebra"
 AccessorsStaticArraysExt = "StaticArrays"
 AccessorsStructArraysExt = "StructArrays"
+AccessorsTestExt = "Test"
 
 [compat]
 AxisKeys = "0.2"
diff --git a/ext/AccessorsDatesExt.jl b/ext/AccessorsDatesExt.jl
new file mode 100644
index 00000000..392f5276
--- /dev/null
+++ b/ext/AccessorsDatesExt.jl
@@ -0,0 +1,37 @@
+module AccessorsDatesExt
+
+using Accessors
+import Accessors: set
+using Dates
+
+set(x::DateTime, ::Type{Date}, y) = DateTime(y, Time(x))
+set(x::DateTime, ::Type{Time}, y) = DateTime(Date(x), y)
+set(x::T, ::Type{T}, y) where {T <: Union{Date, Time}} = y
+
+# directly mirrors Dates.value implementation in stdlib
+set(x::Date, ::typeof(Dates.value), y) = @set x.instant.periods.value = y
+set(x::DateTime, ::typeof(Dates.value), y) = @set x.instant.periods.value = y
+set(x::Time, ::typeof(Dates.value), y) = @set x.instant.value = y
+
+set(x::Date, ::typeof(year),                    y) = Date(y,       month(x), day(x))
+set(x::Date, ::typeof(month),                   y) = Date(year(x),        y, day(x))
+set(x::Date, ::typeof(day),                     y) = Date(year(x), month(x),      y)
+set(x::Date, ::typeof(yearmonth),    y::NTuple{2}) = Date(y...,              day(x))
+set(x::Date, ::typeof(monthday),     y::NTuple{2}) = Date(year(x),             y...)
+set(x::Date, ::typeof(yearmonthday), y::NTuple{3}) = Date(y...)
+set(x::Date, ::typeof(dayofweek),               y) = firstdayofweek(x) + Day(y - 1)
+
+set(x::Time, ::typeof(hour),        y) = Time(y,       minute(x), second(x), millisecond(x), microsecond(x), nanosecond(x))
+set(x::Time, ::typeof(minute),      y) = Time(hour(x),         y, second(x), millisecond(x), microsecond(x), nanosecond(x))
+set(x::Time, ::typeof(second),      y) = Time(hour(x), minute(x),         y, millisecond(x), microsecond(x), nanosecond(x))
+set(x::Time, ::typeof(millisecond), y) = Time(hour(x), minute(x), second(x),              y, microsecond(x), nanosecond(x))
+set(x::Time, ::typeof(microsecond), y) = Time(hour(x), minute(x), second(x), millisecond(x),              y, nanosecond(x))
+set(x::Time, ::typeof(nanosecond),  y) = Time(hour(x), minute(x), second(x), millisecond(x), microsecond(x),             y)
+
+set(x::DateTime, optic::Union{typeof.((year, month, day, yearmonth, monthday, yearmonthday, dayofweek))...}, y) = modify(d -> set(d, optic, y), x, Date)
+set(x::DateTime, optic::Union{typeof.((hour, minute, second, millisecond))...}, y) = modify(d -> set(d, optic, y), x, Time)
+
+
+set(x::AbstractString, optic::Base.Fix2{Type{T}}, dt::T) where {T <: Union{Date, Time, DateTime}} = Dates.format(dt, optic.x)
+
+end
diff --git a/ext/AccessorsLinearAlgebraExt.jl b/ext/AccessorsLinearAlgebraExt.jl
new file mode 100644
index 00000000..9904475a
--- /dev/null
+++ b/ext/AccessorsLinearAlgebraExt.jl
@@ -0,0 +1,9 @@
+module AccessorsLinearAlgebraExt
+
+import Accessors: set
+using LinearAlgebra: norm, normalize
+
+set(arr, ::typeof(normalize), val) = norm(arr) * val
+set(arr, ::typeof(norm), val)      = map(Base.Fix2(*, val / norm(arr)), arr) # should we check val is positive?
+
+end
diff --git a/ext/AccessorsTestExt.jl b/ext/AccessorsTestExt.jl
new file mode 100644
index 00000000..f69bc41c
--- /dev/null
+++ b/ext/AccessorsTestExt.jl
@@ -0,0 +1,44 @@
+module AccessorsTestExt
+
+using Accessors
+using Test: @test
+
+function Accessors.test_getset_laws(lens, obj, val1, val2; cmp=(==))
+    # set ⨟ get
+    val = lens(obj)
+    @test cmp(set(obj, lens, val), obj)
+
+    # get ⨟ set
+    obj1 = set(obj, lens, val1)
+    @test cmp(lens(obj1), val1)
+
+    # set idempotent
+    obj12 = set(obj1, lens, val2)
+    obj2 = set(obj12, lens, val2)
+    @test cmp(obj12, obj2)
+end
+
+function Accessors.test_modify_law(f, lens, obj)
+    obj_modify = modify(f, obj, lens)
+    old_val = lens(obj)
+    val = f(old_val)
+    obj_setfget = set(obj, lens, val)
+    @test obj_modify == obj_setfget
+end
+
+function Accessors.test_getsetall_laws(optic, obj, vals1, vals2; cmp=(==))
+    # setall ⨟ getall
+    vals = getall(obj, optic)
+    @test cmp(setall(obj, optic, vals), obj)
+
+    # getall ⨟ setall
+    obj1 = setall(obj, optic, vals1)
+    @test cmp(collect(getall(obj1, optic)), collect(vals1))
+
+    # setall idempotent
+    obj12 = setall(obj1, optic, vals2)
+    obj2 = setall(obj12, optic, vals2)
+    @test obj12 == obj2
+end
+
+end
diff --git a/src/Accessors.jl b/src/Accessors.jl
index 0a1cc2a7..d23f319e 100644
--- a/src/Accessors.jl
+++ b/src/Accessors.jl
@@ -20,4 +20,10 @@ include("sugar.jl")
 include("functionlenses.jl")
 include("testing.jl")
 
+@static if !isdefined(Base, :get_extension)
+    include("../ext/AccessorsDatesExt.jl")
+    include("../ext/AccessorsLinearAlgebraExt.jl")
+    include("../ext/AccessorsTestExt.jl")
+end
+
 end
diff --git a/src/functionlenses.jl b/src/functionlenses.jl
index 1f5911b7..a3eb8888 100644
--- a/src/functionlenses.jl
+++ b/src/functionlenses.jl
@@ -1,6 +1,3 @@
-using LinearAlgebra: norm, normalize
-using Dates
-
 # first and last on general indexable collections
 set(obj, ::typeof(first), val) = @set obj[firstindex(obj)] = val
 set(obj, ::typeof(last), val) = @set obj[lastindex(obj)] = val
@@ -132,46 +129,10 @@ set(x, f::Base.Fix2{typeof(rem)}, y) = set(x, @optic(last(divrem(_, f.x))), y)
 
 set(x::AbstractString, f::Base.Fix1{typeof(parse), Type{T}}, y::T) where {T} = string(y)
 
-set(arr, ::typeof(normalize), val) = norm(arr) * val
-set(arr, ::typeof(norm), val)      = map(Base.Fix2(*, val / norm(arr)), arr) # should we check val is positive?
-
 set(f, ::typeof(inverse), invf) = setinverse(f, invf)
 
-set(obj, ::typeof(Base.splat(atan)), val) = @set Tuple(obj) = norm(obj) .* sincos(val)
-set(obj, ::typeof(Base.splat(hypot)), val) = @set norm(obj) = val
-
-################################################################################
-##### dates
-################################################################################
-set(x::DateTime, ::Type{Date}, y) = DateTime(y, Time(x))
-set(x::DateTime, ::Type{Time}, y) = DateTime(Date(x), y)
-set(x::T, ::Type{T}, y) where {T <: Union{Date, Time}} = y
-
-# directly mirrors Dates.value implementation in stdlib
-set(x::Date, ::typeof(Dates.value), y) = @set x.instant.periods.value = y
-set(x::DateTime, ::typeof(Dates.value), y) = @set x.instant.periods.value = y
-set(x::Time, ::typeof(Dates.value), y) = @set x.instant.value = y
-
-set(x::Date, ::typeof(year),                    y) = Date(y,       month(x), day(x))
-set(x::Date, ::typeof(month),                   y) = Date(year(x),        y, day(x))
-set(x::Date, ::typeof(day),                     y) = Date(year(x), month(x),      y)
-set(x::Date, ::typeof(yearmonth),    y::NTuple{2}) = Date(y...,              day(x))
-set(x::Date, ::typeof(monthday),     y::NTuple{2}) = Date(year(x),             y...)
-set(x::Date, ::typeof(yearmonthday), y::NTuple{3}) = Date(y...)
-set(x::Date, ::typeof(dayofweek),               y) = firstdayofweek(x) + Day(y - 1)
-
-set(x::Time, ::typeof(hour),        y) = Time(y,       minute(x), second(x), millisecond(x), microsecond(x), nanosecond(x))
-set(x::Time, ::typeof(minute),      y) = Time(hour(x),         y, second(x), millisecond(x), microsecond(x), nanosecond(x))
-set(x::Time, ::typeof(second),      y) = Time(hour(x), minute(x),         y, millisecond(x), microsecond(x), nanosecond(x))
-set(x::Time, ::typeof(millisecond), y) = Time(hour(x), minute(x), second(x),              y, microsecond(x), nanosecond(x))
-set(x::Time, ::typeof(microsecond), y) = Time(hour(x), minute(x), second(x), millisecond(x),              y, nanosecond(x))
-set(x::Time, ::typeof(nanosecond),  y) = Time(hour(x), minute(x), second(x), millisecond(x), microsecond(x),             y)
-
-set(x::DateTime, optic::Union{typeof.((year, month, day, yearmonth, monthday, yearmonthday, dayofweek))...}, y) = modify(d -> set(d, optic, y), x, Date)
-set(x::DateTime, optic::Union{typeof.((hour, minute, second, millisecond))...}, y) = modify(d -> set(d, optic, y), x, Time)
-
-
-set(x::AbstractString, optic::Base.Fix2{Type{T}}, dt::T) where {T <: Union{Date, Time, DateTime}} = Dates.format(dt, optic.x)
+set(obj, ::typeof(Base.splat(atan)), val) = @set Tuple(obj) = hypot(obj...) .* sincos(val)
+set(obj, ::typeof(Base.splat(hypot)), val) = map(Base.Fix2(*, val / hypot(obj...)), obj)
 
 ################################################################################
 ##### strings
diff --git a/src/testing.jl b/src/testing.jl
index e5f356a9..2687a6ae 100644
--- a/src/testing.jl
+++ b/src/testing.jl
@@ -1,40 +1,5 @@
-using Test: @test
-function test_getset_laws(lens, obj, val1, val2; cmp=(==))
-
-    # set ⨟ get
-    val = lens(obj)
-    @test cmp(set(obj, lens, val), obj)
-
-    # get ⨟ set
-    obj1 = set(obj, lens, val1)
-    @test cmp(lens(obj1), val1)
-
-    # set idempotent
-    obj12 = set(obj1, lens, val2)
-    obj2 = set(obj12, lens, val2)
-    @test cmp(obj12, obj2)
-end
-
-function test_modify_law(f, lens, obj)
-    obj_modify = modify(f, obj, lens)
-    old_val = lens(obj)
-    val = f(old_val)
-    obj_setfget = set(obj, lens, val)
-    @test obj_modify == obj_setfget
-end
-
-function test_getsetall_laws(optic, obj, vals1, vals2; cmp=(==))
-
-    # setall ⨟ getall
-    vals = getall(obj, optic)
-    @test cmp(setall(obj, optic, vals), obj)
-
-    # getall ⨟ setall
-    obj1 = setall(obj, optic, vals1)
-    @test cmp(collect(getall(obj1, optic)), collect(vals1))
-
-    # setall idempotent
-    obj12 = setall(obj1, optic, vals2)
-    obj2 = setall(obj12, optic, vals2)
-    @test obj12 == obj2
-end
+# placeholders only
+# actual definitions in ext/AccessorsTestExt.jl
+function test_getset_laws end
+function test_modify_law end
+function test_getsetall_laws end