Implement == and hash for IndexLens and ComposedLens

Author: phipsgabler

src/lens.jl

@@ -6,7 +6,7 @@ export setproperties
 export constructorof
 
 
-import Base: get
+import Base: get, hash, ==
 using Base: getproperty
 
 """
@@ -99,6 +99,7 @@ struct IdentityLens <: Lens end
 get(obj, ::IdentityLens) = obj
 set(obj, ::IdentityLens, val) = val
 
+
 struct PropertyLens{fieldname} <: Lens end
 
 function get(obj, l::PropertyLens{field}) where {field}
@@ -115,6 +116,11 @@ struct ComposedLens{LO, LI} <: Lens
     inner::LI
 end
 
+function ==(l1::ComposedLens{LO, LI}, l2::ComposedLens{LO, LI}) where {LO, LI}
+    return l1.outer == l2.outer && l1.inner == l2.inner
+end
+hash(l::ComposedLens, h::UInt) = hash(l.outer, hash(l.inner, hash(:ComposedLens, h)))
+
 """
     compose([lens₁, [lens₂, [lens₃, ...]]])
 
@@ -173,6 +179,8 @@ end
 struct IndexLens{I <: Tuple} <: Lens
     indices::I
 end
+==(l1::IndexLens{I}, l2::IndexLens{I}) where {I} = l1.indices == l2.indices
+hash(l::IndexLens, h::UInt) = hash(l.indices, hash(:IndexLens, h))
 
 Base.@propagate_inbounds function get(obj, l::IndexLens)
     getindex(obj, l.indices...)

test/test_core.jl

@@ -205,6 +205,26 @@ end
     end
 end
 
+@testset "equality & hashing" begin
+    # singletons (identity and property lens) are object equal
+    for (l, r) ∈ [
+        @lens(_) => @lens(_),
+        @lens(_.a) => @lens(_.a)
+    ]
+        @test l === r
+    end
+
+    # composite and index lenses are structurally equal
+    for (l, r) ∈ [
+        @lens(_[1]) => @lens(_[1])
+        @lens(_.a[2]) => @lens(_.a[2])
+    ]
+        @test l == r
+        @test hash(l) == hash(r)
+    end
+end
+
+
 @testset "type stability" begin
     o1 = 2
     o22 = 2