Add isnothing (#29679)

Author: kescobo

NEWS.md

@@ -5,6 +5,7 @@ New language features
 ---------------------
 
   * `CartesianIndices` can now be constructed from two `CartesianIndex`es `I` and `J` with `I:J` ([#29440]).
+  * `isnothing(::Any)` function can now be called to check whether something is a `Nothing`, returns a `Bool` ([#29679])
 
 Language changes
 ----------------

base/exports.jl

@@ -669,6 +669,7 @@ export
     missing,
     skipmissing,
     something,
+    isnothing,
 
 # time
     sleep,

base/some.jl

@@ -40,6 +40,15 @@ Throw an error if `x === nothing`, and return `x` if not.
 notnothing(x::Any) = x
 notnothing(::Nothing) = throw(ArgumentError("nothing passed to notnothing"))
 
+"""
+    isnothing(x)
+
+Return `true` if `x === nothing`, and return `false` if not.
+"""
+isnothing(::Any) = false
+isnothing(::Nothing) = true
+
+
 """
     something(x, y...)
 

doc/src/base/base.md

@@ -199,6 +199,7 @@ Core.NamedTuple
 Base.Val
 Core.Vararg
 Core.Nothing
+Base.isnothing
 Base.Some
 Base.something
 Base.Enums.@enum

test/some.jl

@@ -94,3 +94,7 @@ b = [ "replacement", "replacement", nothing, missing ]
 using Base: notnothing
 @test notnothing(1) === 1
 @test_throws ArgumentError notnothing(nothing)
+
+# isnothing()
+@test !isnothing(1)
+@test isnothing(nothing)