add rand(::Type{<:Pair}

stdlib/Random/src/Random.jl

@@ -290,7 +290,7 @@ Pick a random element or array of random elements from the set of values specifi
 * a string (considered as a collection of characters), or
 * a type: the set of values to pick from is then equivalent to `typemin(S):typemax(S)` for
   integers (this is not applicable to [`BigInt`](@ref)), and to ``[0, 1)`` for floating
-  point numbers;
+  point numbers; `S` can also be a `Pair` type, in which case random pairs are produced;
 
 `S` defaults to [`Float64`](@ref)
 (except when `dims` is a tuple of integers, in which case `S` must be specified).

stdlib/Random/src/generation.jl

@@ -161,6 +161,18 @@ function rand(r::AbstractRNG, ::SamplerType{T}) where {T<:AbstractChar}
     (c < 0xd800) ? T(c) : T(c+0x800)
 end
 
+### random pairs
+
+function Sampler(RNG::Type{<:AbstractRNG}, ::Type{Pair{A,B}}, n::Repetition) where {A,B}
+    sp1 = Sampler(RNG, A, n)
+    sp2 = A === B ? sp1 : Sampler(RNG, B, n)
+    SamplerTag{Tuple{Pair{A,B}}}(sp1 => sp2) # Tuple so that the gentype is Pair{A,B}
+                                             # in SamplerTag's constructor
+end
+
+rand(rng::AbstractRNG, sp::SamplerTag{<:Tuple{<:Pair}}) =
+    rand(rng, sp.data.first) => rand(rng, sp.data.second)
+
 
 ## Generate random integer within a range
 

stdlib/Random/test/runtests.jl

@@ -686,3 +686,9 @@ end
     @test Random.gentype(Random.UInt52(UInt128)) == UInt128
     @test Random.gentype(Random.UInt104()) == UInt128
 end
+
+@testset "rand(::Type{<:Pair})" begin
+    @test rand(Pair{Int,Int}) isa Pair{Int,Int}
+    @test rand(Pair{Int,Float64}) isa Pair{Int,Float64}
+    @test rand(Pair{Int,Float64}, 3) isa Array{Pair{Int,Float64}}
+end