Allow map!(f, array) (#40632)

...there's really no sensible interpretation of `map!(f, array)` other than `map!(f, array, array)`.

---------

Co-authored-by: Lilith Orion Hafner <[email protected]>

Author: mcabbott

NEWS.md

@@ -117,6 +117,7 @@ New library features
 * `invoke` now supports passing a CodeInstance instead of a type, which can enable
 certain compiler plugin workflows ([#56660]).
 * `sort` now supports `NTuple`s ([#54494])
+* `map!(f, A)` now stores the results in `A`, like `map!(f, A, A)`. or `A .= f.(A)` ([#40632]).
 
 Standard library changes
 ------------------------

base/abstractarray.jl

@@ -3503,11 +3503,32 @@ julia> map!(+, zeros(Int, 5), 100:999, 1:3)
 ```
 """
 function map!(f::F, dest::AbstractArray, As::AbstractArray...) where {F}
-    isempty(As) && throw(ArgumentError(
-        """map! requires at least one "source" argument"""))
+    @assert !isempty(As) # should dispatch to map!(f, A)
     map_n!(f, dest, As)
 end
 
+"""
+    map!(function, array)
+
+Like [`map`](@ref), but stores the result in the same array.
+!!! compat "Julia 1.12"
+    This method requires Julia 1.12 or later. To support previous versions too,
+    use the equivalent `map!(function, array, array)`.
+
+# Examples
+```jldoctest
+julia> a = [1 2 3; 4 5 6];
+
+julia> map!(x -> x^3, a);
+
+julia> a
+2×3 Matrix{$Int}:
+  1    8   27
+ 64  125  216
+```
+"""
+map!(f::F, inout::AbstractArray) where F = map!(f, inout, inout)
+
 """
     map(f, A::AbstractArray...) -> N-array
 

test/abstractarray.jl

@@ -908,7 +908,7 @@ test_ind2sub(TestAbstractArray)
 
 include("generic_map_tests.jl")
 generic_map_tests(map, map!)
-@test_throws ArgumentError map!(-, [1])
+@test map!(-, [1]) == [-1]
 
 test_UInt_indexing(TestAbstractArray)
 test_13315(TestAbstractArray)