On Tuesday, 18 June 2019 at 12:26:14 UTC, lili wrote:
Hi guys:
   Is the Dlang fix-length array alloc on stack?  when a test
    writeln([1]).sizeof //16
    writeln([2]).sizeof //16
    Why, What is the fix-length array memory layout.

You are quite confused...

[...] is an array literal, not a static array. Those aren't the same thing.

When you pass a array literal anywhere in your code, it will in principle be referred as a slice variable. This will not reallocate the contents. However the slice reference is another variable that takes up two words of space (see code below).

This slice type is the same variable type that stores dynamic arrays -- be they allocated or null.

Array literals are not necessarily allocated. The compiler is free to embed them into the program machine code itself.

If you want a static array, you can just declare it directly e.g. int[n] arr. Of course you can also generate is out of an array literal with the staticArray std library function.

PS the layout of D arrays is of course linear and contiguous. Both static or dynamic, just like C/C++ static arrays or std::vectors respectively.

Hopefully this code makes things clear:

enum lenInts = int.sizeof;
static assert(lenInts == 4);

int[1] arrStatic;
static assert(lenInts == arrStatic.sizeof);

auto slice = arrStatic[];
alias sliceType = typeof(slice);
static assert(is(sliceType == int[]));

enum lenPointers = size_t.sizeof; // fyi (unsinged) pointers
static assert(ptrdiff_t.sizeof == lenPointers); // fyi signed pointer diff

static assert(sliceType.sizeof == 2 * lenPointers);
// because a D array reference remembers a pointer (like C) plus the length (stored in a word-length integer)

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