Ignore identity optic when composing (#96)

Author: sunxd3

Project.toml

@@ -3,7 +3,7 @@ uuid = "7a57a42e-76ec-4ea3-a279-07e840d6d9cf"
 keywords = ["probablistic programming"]
 license = "MIT"
 desc = "Common interfaces for probabilistic programming"
-version = "0.8.2"
+version = "0.8.3"
 
 [deps]
 AbstractMCMC = "80f14c24-f653-4e6a-9b94-39d6b0f70001"

src/varname.jl

@@ -150,7 +150,14 @@ end
 
 # Allow compositions with optic.
 function Base.:∘(optic::ALLOWED_OPTICS, vn::VarName{sym,<:ALLOWED_OPTICS}) where {sym}
-    return VarName{sym}(optic ∘ getoptic(vn))
+    vn_optic = getoptic(vn)
+    if vn_optic == identity
+        return VarName{sym}(optic)
+    elseif optic == identity
+        return vn
+    else
+        return VarName{sym}(optic ∘ vn_optic)
+    end
 end
 
 Base.hash(vn::VarName, h::UInt) = hash((getsym(vn), getoptic(vn)), h)

test/varname.jl

@@ -53,6 +53,13 @@ end
     @testset "compose and opcompose" begin
         @test IndexLens(1) ∘ @varname(x.a) == @varname(x.a[1])
         @test @varname(x.a) ⨟ IndexLens(1) == @varname(x.a[1])
+
+        @test @varname(x) ⨟ identity == @varname(x)
+        @test identity ∘ @varname(x) == @varname(x)
+        @test @varname(x.a) ⨟ identity == @varname(x.a)
+        @test identity ∘ @varname(x.a) == @varname(x.a)
+        @test @varname(x[1].b) ⨟ identity == @varname(x[1].b)
+        @test identity ∘ @varname(x[1].b) == @varname(x[1].b)
     end
 
     @testset "get & set" begin