Bug 2101 – CTFE: Please may I use mutable arrays at compile time?

The docs say I can't use non-const arrays at compile-time. But I want to, so this is an enhancement request. The following does not compile. int ctfeTest() { char[10] a; // <--- PROBLEM return 1; } const int A = ctfeTest(); This does int ctfeTest() { char[] a; // <--- OK return 1; } but that's completely pointless. This doesn't: int ctfeTest() { char[] a = new char[10]; // <--- PROBLEM return 1; } Nor does this: int ctfeTest() { char[] a; a.length = 10; // <--- PROBLEM return 1; } Even if we can't have dynamic arrays, what's the harm with static ones?

You could use something like this (quickly hacked, dmd 1.029): T[] newCtfeArray(T)(size_t size) { T[] array; if (!size) return array; array ~= T.init; if (array.length < size) return newCtfeArray(array, size); return array; } private T[] newCtfeArray(T, U = void)(T[] array, size_t size) { while (array.length * 2 <= size) array ~= array; if (array.length < size) return array ~= newCtfeArray!(T)(size - array.length); return array; } int[] test() { // Allocate an array of 123 ints. The memory will not be freed, sigh auto a = newCtfeArray!(int)(123); foreach (i, e; a) { a[i] = e; } return a; } void main() { static const a = test(); }

On 12/05/2008, [email protected] <[email protected]> wrote: > You could use something like this (quickly hacked, dmd 1.029): That's very clever! But somehow, I'll be giving that a miss. What I was really after is to be able to use new to allocate them, and to change the length by modifying .length. That way, a good deal of existing code could magically start working at compile time, without having to rewrite it. Also, I don't believe there's any way to do static if(code will be used in CTFE) { /* clever workarounds */ } else { /* real D */ } (Not that I'd want that, but it would at least make the clever workarounds CTFE-only).

Janice's first case has compiled for quite a long time now. The third case, involving 'new', is very straightforward. The final case (changing length) is doubtful whether it is a good idea. I think with implementing 'new', we can close this bug. PATCH to allow dynamic array creation with new. Insert this code into interpret.c, around line 2690. Also add the declaration for it in NewExp in expression.h. Also need to change the spec to remove the restriction on using 'new'. ------------ Expression *NewExp::interpret(InterState *istate) { #if LOG printf("NewExp::interpret() %s\n", toChars()); #endif if (newtype->ty == Tarray && arguments && arguments->dim == 1) { Expression *lenExpr = ((Expression *)(arguments->data[0]))->interpret(istate); if (lenExpr == EXP_CANT_INTERPRET) return EXP_CANT_INTERPRET; return createBlockDuplicatedArrayLiteral(newtype, newtype->defaultInitLiteral(), lenExpr->toInteger()); } error("Cannot interpret %s at compile time", toChars()); return EXP_CANT_INTERPRET; }

Changeset 333.

fixed dmd 1.056 and 2.040