Fix missing default type for poisson and geometric template parameter T - #2893
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…tensor-stack#2871) This commit addresses GitHub issue xtensor-stack#2871 where using 'auto' with xtensor reducer functions (like amax, sum with keep_dims) in functions causes crashes or incorrect results in optimized builds. The issue is that lazy expressions hold references to local variables. When intermediate results are stored with 'auto', these references become dangling when the function returns, leading to undefined behavior. Fixes xtensor-stack#2871
- Only force evaluation of the returned expression; intermediate lazy expressions are safe as long as they do not outlive the function - Use auto for shifted/expVals/sumExp in the doc example and tests - Remove misleading "Alternatively" sections (eval on intermediates is not required; evaluation_strategy::immediate does not fix the issue) - Fix logSoftmax_eval test variant to drop unnecessary xt::eval wrappers
A lazy reducer (e.g. xt::sum with keep_dims) cannot be safely used as an operand in a subsequent element-wise expression without first materializing it. Element-wise lazy expressions (shifted, expVals) are safe as auto, but the reducer result (sumExp) must be assigned to xt::xtensor or wrapped in xt::eval before use. This fixes the CI test failure in issue_2871_intermediate_result_handling.
This was referenced May 17, 2026
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xt::random::poisson and xt::random::geometric both use T only internally (as the distribution's output type), so the compiler has no way to deduce it from the call site. Adding = int as the default matches the underlying std::poisson_distribution and std::geometric_distribution defaults and lets users call these functions without spelling out the type every time. Fixes #2884.