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doc: fix type-layout.adoc clarity (u256 hex, enum selector, snapshot) #9766

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doc: fix type-layout.adoc clarity (u256 hex, enum selector, snapshot) #9766

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13 changes: 7 additions & 6 deletions ...ference/src/components/cairo/modules/language_constructs/pages/type-layout.adoc
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Expand Up @@ -88,10 +88,10 @@ A u256 value is stored across two cells. For example, the value `500` is stored
- Cell 0 (low): `500`
- Cell 1 (high): `0`

For a full 256-bit value, you need a 64-digit hex number. The value
`0x123456789ABCDEF0FEDCBA9876543210123456789ABCDEF0FEDCBA9876543210` is stored as:
- Cell 0 (low): `0x123456789ABCDEF0FEDCBA9876543210` (lower 128 bits)
- Cell 1 (high): `0x123456789ABCDEF0FEDCBA9876543210` (upper 128 bits)
For a full 256-bit value like
`0xAAAAAAAABBBBBBBBCCCCCCCCDDDDDDDD00000000111111112222222233333333`, it is stored as:
- Cell 0 (low): `0x00000000111111112222222233333333` (lower 128 bits)
- Cell 1 (high): `0xAAAAAAAABBBBBBBBCCCCCCCCDDDDDDDD` (upper 128 bits)

== Enum Layout

Expand All @@ -117,7 +117,7 @@ For `Option<u256>`:
=== Variant Selector Encoding

- **1-2 variants:** Selector is the variant index (0 or 1)
- **3+ variants:** Selector uses a jump table encoding
- **3+ variants:** Selector is a felt252-encoded jump offset used by the runtime

Example with multiple variants:

Expand Down Expand Up @@ -182,7 +182,8 @@ let x: u256 = 100;
let snap: @u256 = @x; // Size: 2 (same as u256)
----

Snapshots enable `Copy` semantics by storing the full value at a snapshot point in memory.
A snapshot is a full copy of the value at the point it was taken, not a pointer or reference.
This is what enables snapshots to be freely `Copy`-able regardless of whether `T` is `Copy`.

=== Nullable<T>

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