Merge pull request #56 from JuliaML/darsnack/fallbacks

Add generic fallbacks for getobs and numobs

src/observation.jl

@@ -2,17 +2,24 @@
     numobs(data)
 
 Return the total number of observations contained in `data`.
+If `data` does not have `numobs` defined, then this function
+falls back to `length(data)`.
 
 See also [`getobs`](@ref)
 """
 function numobs end
 
+# Generic Fallbacks
+numobs(data) = length(data)
+
 """
     getobs(data, [idx])
 
 Return the observations corresponding to the observation-index `idx`.
 Note that `idx` can be any type as long as `data` has defined
 `getobs` for that type.
+If `data` does not have `getobs` defined, then this function
+falls back to `data[idx]`.
 
 The returned observation(s) should be in the form intended to
 be passed as-is to some learning algorithm. There is no strict
@@ -29,7 +36,7 @@ function getobs end
 
 # Generic Fallbacks
 getobs(data) = data
-# getobs(data, idx) = data[idx]
+getobs(data, idx) = data[idx]
 
 """
     getobs!(buffer, data, idx)

test/observation.jl

@@ -1,3 +1,9 @@
+@testset "fallbacks" begin
+    x = FallbackType()
+    @test getobs(x, 3) == 1234
+    @test numobs(x) == 5678
+end
+
 @testset "array" begin
     a = rand(2,3)
     @test numobs(a) == 3

test/runtests.jl

@@ -31,6 +31,10 @@ const Y1 = collect(1:15)
 
 struct EmptyType end
 
+struct FallbackType end
+Base.getindex(::FallbackType, i) = 1234
+Base.length(::FallbackType) = 5678
+
 struct CustomType end
 MLUtils.numobs(::CustomType) = 15
 MLUtils.getobs(::CustomType, i::Int) = i