Throw ArgumentError not plain ErrorException

base/iterators.jl

@@ -1097,30 +1097,32 @@ length(s::Stateful) = length(s.itr) - s.taken
 """
     only(x)
 
-Returns the one and only element of collection `x`, and throws an error if the collection
-has zero or multiple elements.
+Returns the one and only element of collection `x`, and throws an `ArgumentError` if the
+collection has zero or multiple elements.
 """
 Base.@propagate_inbounds function only(x)
     i = iterate(x)
     @boundscheck if i === nothing
-        error("Collection is empty, must contain exactly 1 element")
+        throw(ArgumentError("Collection is empty, must contain exactly 1 element"))
     end
     (ret, state) = i
     j = iterate(x, state)
     @boundscheck if j !== nothing
-        error("Collection has multiple elements, must contain exactly 1 element")
+        throw(ArgumentError("Collection has multiple elements, must contain exactly 1 element"))
     end
     return ret
 end
 
 # Collections of known size
-only(x::Tuple{}) = error("Tuple is empty, must contain exactly 1 element")
+only(x::Tuple{}) = throw(ArgumentError("Tuple is empty, must contain exactly 1 element")
 only(x::Tuple{Any}) = x[1]
-only(x::Tuple) = error("Tuple contains $(length(x)) elements, must contain exactly 1 element")
-
+only(x::Tuple) = throw(
+    ArgumentError("Tuple contains $(length(x)) elements, must contain exactly 1 element")
+)
 only(a::AbstractArray{<:Any, 0}) = @inbounds return a[]
-
 only(x::NamedTuple{<:Any, <:Tuple{Any}}) = first(x)
-only(x::NamedTuple) = error("NamedTuple contains $(length(x)) elements, must contain exactly 1 element")
+only(x::NamedTuple) = throw(
+    ArgumentError("NamedTuple contains $(length(x)) elements, must contain exactly 1 element")
+)
 
 end

test/iterators.jl

@@ -183,7 +183,6 @@ end
 @test Base.IteratorEltype(repeated(0, 5)) == Base.HasEltype()
 @test Base.IteratorSize(zip(repeated(0), repeated(0))) == Base.IsInfinite()
 
-
 # product
 # -------
 
@@ -411,7 +410,6 @@ for n in [5,6]
           [(1,1),(2,2),(3,3),(4,4),(5,5)]
 end
 
-
 @test join(map(x->string(x...), partition("Hello World!", 5)), "|") ==
       "Hello| Worl|d!"
 
@@ -650,22 +648,22 @@ end
 
 @testset "only" begin
     @test only([3]) === 3
-    @test_throws ErrorException only([])
-    @test_throws ErrorException only([3, 2])
+    @test_throws ArgumentError only([])
+    @test_throws ArgumentError only([3, 2])
 
     @test @inferred(only((3,))) === 3
-    @test_throws ErrorException only(())
-    @test_throws ErrorException only((3, 2))
+    @test_throws ArgumentError only(())
+    @test_throws ArgumentError only((3, 2))
 
     @test only(Dict(1=>3)) === (1=>3)
-    @test_throws ErrorException only(Dict{Int,Int}())
-    @test_throws ErrorException only(Dict(1=>3, 2=>2))
+    @test_throws ArgumentError only(Dict{Int,Int}())
+    @test_throws ArgumentError only(Dict(1=>3, 2=>2))
 
     @test only(Set([3])) === 3
-    @test_throws ErrorException only(Set(Int[]))
-    @test_throws ErrorException only(Set([3,2]))
+    @test_throws ArgumentError only(Set(Int[]))
+    @test_throws ArgumentError only(Set([3,2]))
 
     @test @inferred(only((;a=1))) === 1
-    @test_throws ErrorException only(NamedTuple())
-    @test_throws ErrorException only((a=3, b=2.0))
+    @test_throws ArgumentError only(NamedTuple())
+    @test_throws ArgumentError only((a=3, b=2.0))
 end