bkietz commented on code in PR #40396:
URL: https://github.com/apache/arrow/pull/40396#discussion_r1519826972
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cpp/src/arrow/compute/expression.cc:
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@@ -845,7 +845,8 @@ Result<Expression> FoldConstants(Expression expr) {
std::move(expr), [](Expression expr) { return expr; },
[](Expression expr, ...) -> Result<Expression> {
auto call = CallNotNull(expr);
- if (std::all_of(call->arguments.begin(), call->arguments.end(),
+ if (!call->arguments.empty() &&
Review Comment:
> So maybe we can implement is_impure property by return
Function::arity().num_args == 0 && Function::arity().is_varargs == false rather
than overridden for every impure function?
I don't think that's viable; for example there may be a UDF which is impure
but still takes arguments.
> There could be `pure` functions called with zero arguments
For example, a UDF `third_party_magic_number()` which takes no arguments but
always returns a compile time constant is pure since the return value is
identical for identical arguments. In this example, we should be able to fold
the filter expression `add(third_party_magic_number(), 42) >= 777` into a
boolean scalar, potentially skipping a lot of scanning
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