added iszero (#305)

Author: stevengj

README.md

@@ -98,9 +98,11 @@ Currently, the `@compat` macro supports the following syntaxes:
 * `transcode` converts between UTF-xx string encodings in Julia 0.5 (as a lightweight
    alternative to the LegacyStrings package) ([#17323])
 
-* `∘` (typically used infix as `f ∘ g`) for function composition can be used in 0.5 and earlier. [#17155](https://github.com/JuliaLang/julia/pull/17155)
+* `∘` (typically used infix as `f ∘ g`) for function composition can be used in 0.5 and earlier ([#17155])
 
-* The method of `!` to negate functions (typically used as a unary operator, as in `!isinteger`) can be used in 0.5 and earlier. [#17155](https://github.com/JuliaLang/julia/pull/17155)
+* The method of `!` to negate functions (typically used as a unary operator, as in `!isinteger`) can be used in 0.5 and earlier ([#17155]).
+
+* `iszero(x)` efficiently checks whether `x == zero(x)` (including arrays) can be used in 0.5 and earlier ([#19950]).
 
 ## Renamed functions
 
@@ -266,6 +268,7 @@ includes this fix. Find the minimum version from there.
 [#16563]: https://github.com/JuliaLang/julia/issues/16563
 [#16603]: https://github.com/JuliaLang/julia/issues/16603
 [#16972]: https://github.com/JuliaLang/julia/issues/16972
+[#17155]: https://github.com/JuliaLang/julia/issues/17155
 [#17302]: https://github.com/JuliaLang/julia/issues/17302
 [#17323]: https://github.com/JuliaLang/julia/issues/17323
 [#17510]: https://github.com/JuliaLang/julia/issues/17510
@@ -275,3 +278,4 @@ includes this fix. Find the minimum version from there.
 [#18977]: https://github.com/JuliaLang/julia/issues/18977
 [#19088]: https://github.com/JuliaLang/julia/issues/19088
 [#19246]: https://github.com/JuliaLang/julia/issues/19246
+[#19950]: https://github.com/JuliaLang/julia/issues/19950

src/Compat.jl

@@ -1708,6 +1708,14 @@ if !isdefined(Base, :numerator)
     export numerator, denominator
 end
 
+# julia #19950
+if !isdefined(Base, :iszero)
+    iszero(x) = x == zero(x)
+    iszero(x::Number) = x == 0
+    iszero(x::AbstractArray) = all(iszero, x)
+    export iszero
+end
+
 # julia#19088
 if VERSION < v"0.6.0-dev.1256"
     Base.take!(io::Base.AbstractIOBuffer) = takebuf_array(io)

test/runtests.jl

@@ -1570,6 +1570,22 @@ let str = randstring(20)
     @test filter(!islower, str) == replace(str, r"[a-z]", "")
 end
 
+# julia#19950, tests from Base (#20028)
+for T in (Float16, Float32, Float64, BigFloat, Int8, Int16, Int32, Int64, Int128,
+          BigInt, UInt8, UInt16, UInt32, UInt64, UInt128)
+    @test iszero(T(0))
+    @test iszero(Complex{T}(0))
+    if T<:Integer
+        @test iszero(Rational{T}(0))
+    end
+    if T<:AbstractFloat
+        @test iszero(T(-0.0))
+        @test iszero(Complex{T}(-0.0))
+    end
+end
+@test !iszero([0, 1, 2, 3])
+@test iszero([0, 0, 0, 0])
+
 x = view(1:10, 2:4)
 D = Diagonal(x)
 @test D[1,1] == 2