> For the complete documentation index, see [llms.txt](https://enma-1.gitbook.io/enma/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://enma-1.gitbook.io/enma/addons/arrays.md).

# Arrays & Vectors

Three carriers, exactly C++: builtin fixed arrays `T a[N]`, heap blocks `new T[N]`, and the library containers `std::vector<T>` / `std::array<T, N>`.

## Builtin fixed arrays — `T a[N]`

```cpp
int64 a[4];                       // frame or file scope
int32 b[3] = {1, 2, 3};           // brace init
char  s[] = "hi";                 // sized from the literal (3 incl. NUL)
int64 m[2][3];                    // 2D, row-major

a[0] = 5;
int64* p = &a[0];                 // decay to element pointer; &a[4] (one past
                                  // the end) is a valid address
```

Elements are contiguous at their natural width (`int8`/`int16`/`int32`/ `float32` pack like C), so a decayed `T*` walks the same bytes natives see. `int8`/`int16` alias `char`/`wchar` — signedness follows the spelling.

Indexing carries **no runtime checks** — an out-of-bounds index is UB, exactly C++. A **provable constant** index outside the bounds is a compile error (`a[4]` on `int64 a[4]`, per-dimension for 2D); the one-past-the-end address `&a[N]` stays legal.

Arrays are not assignable or member-accessible as objects (`a = b`, `a.size()` reject) — use the extent you declared, or a container.

## Heap blocks — `new T[N]` / `delete[]`

```cpp
It* xs = new It[8];               // default-constructs each element
xs[3].v = 7;
delete[] xs;                      // destroys each element, frees the block
```

Runtime-sized (`new T[n]`) works the same. `T*` arithmetic and subscripts use the element stride.

## std::vector\<T>

Growable, contiguous, value-semantic. From the `std` prelude.

```cpp
std::vector<int64> v = {1, 2, 3};
v.push_back(4);
v[0] = 10;                        // T& operator[] — writes go through
for (int64 x : v) { ... }

v.size()   v.empty()   v.capacity()
v.at(i)    v.front()   v.back()
v.data()                          // T* to the buffer
v.reserve(n)   v.resize(n)
v.pop_back()                      // void, exactly C++
v.insert(v.begin() + i, x)        // iterator position
v.erase(v.begin() + i)
v.clear()
v.begin()  v.end()                // iterators: * ++ == and it + n
```

Copying a vector deep-copies its elements; `push_back` copies the argument in (one user copy-constructor fire per push, exactly C++).

## std::array\<T, N>

Fixed-size value struct with C++-exact layout: `sizeof == N * sizeof(T)`, elements at offset 0, usable wherever a flat `T[N]` blob is expected.

```cpp
std::array<int64, 4> a;
a[1] = 5;                         // T& operator[] — unchecked
a.at(9);                          // bounds-checked: throws

a.size()   a.max_size()   a.empty()
a.front()  a.back()
a.data()                          // raw T*
a.fill(x)
a.swap(other)
a.begin()  a.end()
```

## Algorithms (namespace std)

Free function templates — they instantiate only where called:

```cpp
std::sort(v)                      // ascending via the element's operator<
std::sum(v)                       // vector<int64>
std::join(v, ", ")                // vector<string> / vector<int64> / vector<wstring>
std::transform(v, (int64 x) => x * 2)
std::filter(v, (int64 x) => x > 0)
std::any_of(v, pred)   std::all_of(v, pred)
std::next(it)          std::next(it, n)
```


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