Show rationals without //1 when typeinfo <: Rational (#45396)

Co-authored-by: Jeff Bezanson <[email protected]> Co-authored-by: Elliot Saba <[email protected]> Co-authored-by: Lilith Orion Hafner <[email protected]>
JuliaLang · Mar 9, 2023 · 5b2240c · 5b2240c · nanosoldier · Mar 9, 2023
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diff --git a/NEWS.md b/NEWS.md
@@ -42,6 +42,7 @@ Standard library changes
 ------------------------
 
 * `startswith` now supports seekable `IO` streams ([#43055])
+* printing integral `Rational`s will skip the denominator in `Rational`-typed IO context (e.g. in `Arrays`) ([#45396])
 
 #### Package Manager
 

diff --git a/base/rational.jl b/base/rational.jl
@@ -83,6 +83,11 @@ end
 
 function show(io::IO, x::Rational)
  show(io, numerator(x))
+
+ if isone(denominator(x)) && get(io, :typeinfo, Any) <: Rational
+ return
+ end
+
  print(io, "//")
  show(io, denominator(x))
 end

diff --git a/test/rational.jl b/test/rational.jl
@@ -253,6 +253,10 @@ end
  rational2 = Rational(-4500, 9000)
  @test sprint(show, rational1) == "1465//8593"
  @test sprint(show, rational2) == "-1//2"
+ @test sprint(show, -2//2) == "-1//1"
+ @test sprint(show, [-2//2,]) == "Rational{$Int}[-1]"
+ @test sprint(show, MIME"text/plain"(), Union{Int, Rational{Int}}[7 3//6; 6//3 2]) ==
+ "2×2 Matrix{Union{Rational{$Int}, $Int}}:\n 7 1//2\n 2//1 2"
  let
  io1 = IOBuffer()
  write(io1, rational1)