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README: the ndarray axis keyword, and what makes $/ a different setter #888

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tannevaled merged 1 commit into from
Nov 4, 2026
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README: the ndarray axis keyword, and what makes $/ a different setter #888

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10 changes: 9 additions & 1 deletion README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -433,6 +433,11 @@ JRuby**):
(`$LOAD_PATH = []` → `NameError`), the checked ones enforce their type
(`$stdout = nil` → `TypeError: $stdout must have write method, NilClass
given`), and **`trace_var`**/`untrace_var` hook assignment to a global.
The separators are not interchangeable: `$,` and `$\` take `rb_str_setter`
and store what they are handed, while `$/` and `$-0` take MRI's
`deprecated_rs_setter` and store a **frozen plain String** of the same bytes
— so `$/ = s` leaves `s` untouched, `$/.frozen?` is true, and `$/` is not
`s.equal?` unless `s` was already a frozen bare String.
- **Strings:** mutable (reference semantics) with `<<`/concat/replace/prepend/
insert/`[]=`/slice!/the bang methods and `freeze`/`FrozenError`;
interpolation, heredocs (`<<`/`<<-`/`<<~`), `%w`/`%i` and `%q`/`%Q`/`%W`/`%I`
Expand Down Expand Up @@ -532,7 +537,10 @@ JRuby**):
`+ - * / **` with broadcasting (a number on either side),
`sqrt`/`exp`/`log`/`sin`/`cos`/`abs`/`square`/`clip`,
`NDArray.maximum`/`minimum`; reductions `sum`/`mean`/`max`/`min`/`prod`/
`argmax`/`argmin` (whole array, or `(axis, keepdims: true)`) and `cumsum`;
`argmax`/`argmin` (whole array, or along one axis with `keepdims: true`) and
`cumsum` (flattened, or along one axis). The axis may be given positionally
(`a.sum(0)`) or by keyword as NumPy spells it (`a.sum(axis: 0)`); both at
once raises `ArgumentError`;
`matmul`/`dot`/`NDArray.outer`, `NDArray.concatenate`/`stack` (`axis:`);
`shape`/`ndim`/`size`/`to_a` (flat), and `p a` prints NumPy's repr
(`array([[0., 1.], ...])`). Every argument is checked: a wrong count or type
Expand Down
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