On Tuesday, 4 May 2021 at 05:24:11 UTC, Imperatorn wrote:

auto a = [1,2,3] + [4,5,6]; //[5,7,9]

The operation necessitates an allocation and people here don't like hidden allocations.

On Tuesday, 4 May 2021 at 18:53:18 UTC, H. S. Teoh wrote:

auto a = [1,2,3] + [4,5,6]; //[5,7,9]

  E[n] opBinary(string op)(Vec v) {
  	Vec result;
  	mixin("result.impl[] = impl[] "~op~" v.impl[];");
  	return result;
  }

To the high priests of D (I have only written one project in D so far):

What would it take to allow array operations like I said before, without rewriting:

auto a = [1,2,3] + [3,2,1]; //[4,4,4]

Can this be accomplished using templates or a library solution, or do I have to modify the compiler?

Thanks

On Tuesday, 4 May 2021 at 19:44:24 UTC, Imperatorn wrote:

auto a = [1,2,3] + [3,2,1]; //[4,4,4]

C++ allows operator overloading for free-standing operator functions, D does not.

Adding this to the compiler is easy enough. You just rewrite all "+" operators to some internal __add(x,y) template and then default that back to "+", then overload it for anything you want... Clunky, but it should work?

On Tuesday, 4 May 2021 at 19:44:24 UTC, Imperatorn wrote:

auto a = [1,2,3] + [4,5,6]; //[5,7,9]

 E[n] opBinary(string op)(Vec v) {
 	Vec result;
 	mixin("result.impl[] = impl[] "~op~" v.impl[];");
 	return result;
 }

auto a = [1,2,3] + [3,2,1]; //[4,4,4]

Array literals are internal to the compiler. But you can just use something different like v(1,2,3). Heck, you can get even closer using a struct with static opIndex to resemble the look-and-feel of array literals: v[1,2,3]. You can adapt H. S. Teoh's or my approach.

This is how it's done:

// for the array-literal-like syntax
struct v
{
    import std.traits : CommonType;
	
    static Vec!(CommonType!Args, Args.length) opIndex(Args...)(Args args)
    {
        return typeof(return)([args]);
    }
}

// the type of objects you create:
struct Vector(...) { ... } // by H. S. Teoh

void main() @nogc
{
    // Look, ma! No allocations!
    int[3] arr = v[1,2,3] + v[4,5,6];
    assert(arr[0] == 5 && arr[1] == 7 && arr[2] == 9);
}

On Tuesday, 4 May 2021 at 19:44:24 UTC, Imperatorn wrote:

auto a = [1,2,3] + [3,2,1]; //[4,4,4]

I'm by no means a high priest of D. However I'm fairly confident the answer to your question is no.

// Built-in:
int[3] a = [1,2,3] + [3,2,1]; // You can do this.
auto   a = [1,2,3] + [3,2,1]; // But not this.

// With H.S. Teoh's thing:
auto a = v(1,2,3) + v(3,2,1); // You can do this - a is int[3].
auto a = v(1,2,3) + v(3,2,1) + v(42,42,42); // But not this - Error: Invalid array operation.

So if you actually want to make this universal, you would need to modify the compiler.

From my own testing, the compiler actually turns these kinds of expressions into a function call.

int[3] a = [1,2,3] + [3,2,1];

// Gets turned into something like ..

import core.internal.array.operations;
int[3] a;
int[3] __temp1 = [1,2,3];
int[3] __temp2 = [3,2,1];
arrayOp!(int[], int[], int[], "+", "=")(a[], __temp1[], __temp2[], "+", "=");

This also might explain why you can't use auto a = ... (it's not a great excuse).

On Tuesday, 4 May 2021 at 20:16:29 UTC, Ola Fosheim Grøstad wrote:

auto a = [1,2,3] + [3,2,1]; //[4,4,4]

Thanks everyone for all clarifications and examples! I'll experiment a bit and see what makes most sense.

On Saturday, 1 May 2021 at 11:32:47 UTC, Blatnik wrote:

import std;
void main() {
  writeln(typeid([1, 2, 3]));
}

auto array = [1, 2, 3]; // Type deduced as int[], not int[3]

void foo(int[] bar);

foo([1, 2, 3]) // Error: Array literal may cause GC allocation.

related : https://issues.dlang.org/show_bug.cgi?id=21756

On Wednesday, 5 May 2021 at 08:58:41 UTC, user1234 wrote:

I have experimented some and found a few workarounds which might be acceptable.

But, I'm having some weird bug. On dmd and dmd-beta it works, but on dmd-nightly I get:

cannot interpret array literal expression [1, 2, 3] + [3, 2, 1] at compile time

I think this might be a regression?

Like, this works as I want:
https://run.dlang.io/is/rHRiP9

If I use dmd or dmd-beta. But if I change it to dmd-nightly it doesn't :(

😢😢😢