Merge pull request #18736 from ninjin/nin/pairconv

RFC: Pair to Pair conversions

Author: vchuravy

base/operators.jl

@@ -964,6 +964,11 @@ reverse{A,B}(p::Pair{A,B}) = Pair{B,A}(p.second, p.first)
 endof(p::Pair) = 2
 length(p::Pair) = 2
 
+convert{A,B}(::Type{Pair{A,B}}, x::Pair{A,B}) = x
+function convert{A,B}(::Type{Pair{A,B}}, x::Pair)
+    convert(A, x[1]) => convert(B, x[2])
+end
+
 # some operators not defined yet
 global //, >:, <|, hcat, hvcat, ⋅, ×, ∈, ∉, ∋, ∌, ⊆, ⊈, ⊊, ∩, ∪, √, ∛
 

test/operators.jl

@@ -21,6 +21,9 @@ B = [true true false]
 @test reverse(Pair(1,2)) == Pair(2,1)
 @test reverse(Pair("13","24")) == Pair("24","13")
 @test typeof(reverse(Pair{String,Int64}("a",1))) == Pair{Int64,String}
+@test convert(Pair{Float64,Float64}, 17 => 4711) === (17.0 => 4711.0)
+@test convert(Pair{Int,Float64}, 17 => 4711) === (17 => 4711.0)
+@test convert(Pair{Float64,Int}, 17 => 4711) === (17.0 => 4711)
 
 p = 1=>:foo
 @test first(p) == 1