Merge pull request #20317 from pabloferz/pz/unique

Improve inferability of unique

base/set.jl

@@ -123,16 +123,45 @@ julia> unique([1; 2; 2; 6])
  6
 ```
 """
-function unique(C)
-    out = Vector{eltype(C)}()
-    seen = Set{eltype(C)}()
-    for x in C
+function unique(itr)
+    T = _default_eltype(typeof(itr))
+    out = Vector{T}()
+    seen = Set{T}()
+    i = start(itr)
+    if done(itr, i)
+        return out
+    end
+    x, i = next(itr, i)
+    if !isleaftype(T)
+        S = typeof(x)
+        return _unique_from(itr, S[x], Set{S}((x,)), i)
+    end
+    push!(seen, x)
+    push!(out, x)
+    return unique_from(itr, out, seen, i)
+end
+
+_unique_from(itr, out, seen, i) = unique_from(itr, out, seen, i)
+@inline function unique_from{T}(itr, out::Vector{T}, seen, i)
+    while !done(itr, i)
+        x, i = next(itr, i)
+        S = typeof(x)
+        if !(S === T || S <: T)
+            R = typejoin(S, T)
+            seenR = convert(Set{R}, seen)
+            outR = convert(Vector{R}, out)
+            if !in(x, seenR)
+                push!(seenR, x)
+                push!(outR, x)
+            end
+            return _unique_from(itr, outR, seenR, i)
+        end
         if !in(x, seen)
             push!(seen, x)
             push!(out, x)
         end
     end
-    out
+    return out
 end
 
 """

test/sets.jl

@@ -212,6 +212,9 @@ u = unique([1,1,2])
 @test length(u) == 2
 @test unique(iseven, [5,1,8,9,3,4,10,7,2,6]) == [5,8]
 @test unique(n->n % 3, [5,1,8,9,3,4,10,7,2,6]) == [5,1,9]
+# issue 20105
+@test @inferred(unique(x for x in 1:1)) == [1]
+@test unique(x for x in Any[1,1.0])::Vector{Real} == [1]
 
 # allunique
 @test allunique([])