[ViralBShah]

map and broadcast over a sparse array throw a MethodError when the function returns a value of a type that has no zero, such as a String, a Tuple, a Pair or nothing.

using SparseArrays
A = sparse([1.0 0.0; 0.0 2.0])
string.(A)
A .=> 1
map(x -> (x,), A)
map(x -> nothing, A)

Before

string.(A)            MethodError: no method matching zero(::String)
A .=> 1               MethodError: no method matching zero(::Pair{Float64, Int64})
map(x -> (x,), A)     MethodError: no method matching zero(::Tuple{Float64})
map(x -> nothing, A)  MethodError: no method matching zero(::Nothing)

After

string.(A)            ["1.0" "0.0"; "0.0" "2.0"]
A .=> 1               sparse([1, 2, 1, 2], [1, 1, 2, 2], [1.0 => 1, 0.0 => 1, 0.0 => 1, 2.0 => 1], 2, 2)
map(x -> (x,), A)     sparse([1, 2, 1, 2], [1, 1, 2, 2], [(1.0,), (0.0,), (0.0,), (2.0,)], 2, 2)
map(x -> nothing, A)  sparse([1, 2, 1, 2], [1, 1, 2, 2], [nothing, nothing, nothing, nothing], 2, 2)

To choose between the zero-preserving kernel and the one that fills the result, the dispatchers evaluate f at the zeros and call _iszero on the value, which calls zero for anything but a Number. The new _iszeroresult is _iszero for a Number, an AbstractArray or Missing, and for any other value returns false when _iszero throws a MethodError: a value without a zero is not one, and fills the result like any other nonzero. It replaces _iszero wherever f at the zeros is tested: the map! and broadcast! dispatchers, _noshapecheck_map, the zero-argument broadcast!, _diffshape_broadcast and _preserveszeros, where only the call of f stays inside the try. The try is reached only for a non-Number result, so the result types of map(sin, A) and A .+ B are inferred as before.

Left out: a broadcast of two or more arguments where one of them stores every entry, such as string.(A, sparse(ones(2, 2))), still throws MethodError: no method matching zero(::String). That path tests each computed entry for zero, and a tolerant check there would cost every eltype that is not a Number.

Split from #1022.

Written by Claude Code.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.77%. Comparing base (3d6d696) to head (aee01a1).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1055   +/-   ##
=======================================
  Coverage   94.77%   94.77%           
=======================================
  Files          16       16           
  Lines        9913     9917    +4     
=======================================
+ Hits         9395     9399    +4     
  Misses        518      518           

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[ViralBShah]

Reviewed by Codex at aee01a1.

No actionable findings within the dispatcher changes. Results without a defined zero now reach the fill path while the existing numeric, array and missing-value checks retain their behavior. The fully stored multi-argument limitation is explicitly identified in the PR.