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Mention that “every address” ≠ “every pointer” #1761

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merged 3 commits into from
Mar 21, 2025
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Mention that “every address” ≠ “every pointer” #1761

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35126d9
Mention that “every address” ≠ “every pointer”
kpreid Mar 17, 2025
c090f46
Add mention of provenance.
kpreid Mar 20, 2025
7fbcb20
Adjust link.
kpreid Mar 20, 2025
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6 changes: 6 additions & 0 deletions src/types/numeric.md
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Expand Up @@ -40,6 +40,10 @@ r[type.numeric.int.size.usize]
The `usize` type is an unsigned integer type with the same number of bits as the
platform's pointer type. It can represent every memory address in the process.

> [!NOTE]
> While a `usize` can represent every *address*, converting a *pointer* to a `usize` is not necessarily a reversible operation.
> For more information, see the documentation for [type cast expressions], [`std::ptr`], and [provenance][std::ptr#provenance] in particular.

r[type.numeric.int.size.isize]
The `isize` type is a signed integer type with the same number of bits as the
platform's pointer type. The theoretical upper bound on object and array size
Expand All @@ -58,3 +62,5 @@ r[type.numeric.validity]

For every numeric type, `T`, the bit validity of `T` is equivalent to the bit
validity of `[u8; size_of::<T>()]`. An uninitialized byte is not a valid `u8`.

[type cast expressions]: ../expressions/operator-expr.md#type-cast-expressions