A common pattern in a world where null exists is

if (!a)
  a = b;

that is semantically equivalent, if a is a pointer (or if it implements opCast!bool), to D

if (a is null)
  a = b;

I propose the get rid of the statement layer. The two statments (there are more actually) can be a single expression:

a ?= b;

As a new binary assign operator.

On Monday, 30 December 2024 at 15:07:41 UTC, Basile B. wrote:

By te way ?= would be a new lexical token, not ? then =. Really the both.

On Monday, 30 December 2024 at 15:07:41 UTC, Basile B. wrote:

if (!a)
  a = b;

if (a is null)
  a = b;

a ?= b;

https://forum.dlang.org/thread/nmwzohfqqyajahkncreq@forum.dlang.org

On Tuesday, 31 December 2024 at 00:38:56 UTC, monkyyy wrote:

if (!a)
  a = b;

if (a is null)
  a = b;

a ?= b;

I use it since monthes in styx. It's one of the best thing that's possible just right now in D. Otherwise I would not propose it. For a long time I thought optional access was really the shit, but at some point I implemented a programming language, and now I'm pretty sure that is the best niche expression.

On Tuesday, 31 December 2024 at 18:10:52 UTC, Paul Backus wrote:

if (!a)
  a = b;

a ?= b;

ref optAssign(T, U)(ref T dest, U value)
{
    if (!dest) dest = value;
    return dest;
}

unittest
{
    int n;
    int* p;

    n.optAssign(123);
    assert(n == 123);
    n.optAssign(456);
    assert(n == 123);

    p.optAssign(&n);
    assert(*p == 123);
    p.optAssign(new int(456));
    assert(*p == 123);
}

Paul while your template is somewhat equivalent, I have doubts over people using it ;)

The first problem I see is that it will be inline-ed only with certains command line arguments, while the proposed expression does not involved a call, or -O, or -inline.

On Thursday, 2 January 2025 at 16:52:01 UTC, Basile B. wrote:

if (!a)
  a = b;

a ?= b;

ref optAssign(T, U)(ref T dest, U value)
{
    if (!dest) dest = value;
    return dest;
}

unittest
{
    int n;
    int* p;

    n.optAssign(123);
    assert(n == 123);
    n.optAssign(456);
    assert(n == 123);

    p.optAssign(&n);
    assert(*p == 123);
    p.optAssign(new int(456));
    assert(*p == 123);
}

Also people will have to import to make it available, while ?= would just works, out of the box.

On Tuesday, 31 December 2024 at 02:12:59 UTC, Basile B. wrote:

By the way ‘the shit’ means ‘the best’. (https://en.wiktionary.org/wiki/the_shit)

On Monday, 30 December 2024 at 15:07:41 UTC, Basile B. wrote:

if (!a)
  a = b;

if (a is null)
  a = b;

a ?= b;

C# has this as the ?? and ??= operator. I use it sometimes and it’s handy. I don’t care much about its exact syntax (some will suggest ?: for the binary one, but ??= looks a lot better than ?:= IMO).

It should be overloadable, too: opBinary!"??" and opBinaryRight!"??" and opOpAssign!"??" should worl as intended.

It’s also an easy way to chicken out of null sutff:

class C;

C f(int x);
C g(int x);

int n = 42;
C c = f(n) ?? g(n) ?? throw new InvalidOperationException();