add Returns (#751)

Author: mcabbott

Project.toml

@@ -1,6 +1,6 @@
 name = "Compat"
 uuid = "34da2185-b29b-5c13-b0c7-acf172513d20"
-version = "3.34.0"
+version = "3.35.0"
 
 [deps]
 Base64 = "2a0f44e3-6c83-55bd-87e4-b1978d98bd5f"

README.md

@@ -54,6 +54,8 @@ changes in `julia`.
 
 ## Supported features
 
+* `Returns(value)` returns `value` for any arguments ([#39794]) (since Compat 3.35)
+
 * The function `current_exceptions()` has been added to get the current
   exception stack. Julia-1.0 lacks runtime support for full execption stacks,
   so we return only the most recent exception in that case. ([#29901]) (since
@@ -270,3 +272,4 @@ Note that you should specify the correct minimum version for `Compat` in the
 [#35316]: https://github.com/JuliaLang/julia/pull/35316
 [#41076]: https://github.com/JuliaLang/julia/pull/41076
 [#34331]: https://github.com/JuliaLang/julia/pull/34331
+[#39794]: https://github.com/JuliaLang/julia/pull/39794

src/Compat.jl

@@ -1102,6 +1102,25 @@ if VERSION < v"1.7.0-DEV.1106"
     export current_exceptions
 end
 
+# https://github.com/JuliaLang/julia/pull/39794
+if VERSION < v"1.7.0-DEV.793"
+    export Returns
+
+    struct Returns{V} <: Function
+        value::V
+        Returns{V}(value) where {V} = new{V}(value)
+        Returns(value) = new{Core.Typeof(value)}(value)
+    end
+
+    (obj::Returns)(args...; kw...) = obj.value
+    function Base.show(io::IO, obj::Returns)
+        show(io, typeof(obj))
+        print(io, "(")
+        show(io, obj.value)
+        print(io, ")")
+    end
+end
+
 include("iterators.jl")
 include("deprecated.jl")
 

test/runtests.jl

@@ -1144,3 +1144,18 @@ end
         """, sprint(show, excs))
     end
 end
+
+# https://github.com/JuliaLang/julia/pull/39794
+@testset "Returns" begin
+    @test @inferred(Returns(1)()   ) === 1
+    @test @inferred(Returns(1)(23) ) === 1
+    @test @inferred(Returns("a")(2,3)) == "a"
+    @test @inferred(Returns(1)(x=1, y=2)) === 1
+    @test @inferred(Returns(Int)()) === Int
+    @test @inferred(Returns(Returns(1))()) === Returns(1)
+    f = @inferred Returns(Int)
+    @inferred f(1,2)
+    val = [1,2,3]
+    @test Returns(val)(1) === val
+    @test sprint(show, Returns(1.0)) == "Returns{Float64}(1.0)"
+end