optional assignment

[Basile B.]

On Sunday, 2 February 2025 at 03:30:17 UTC, Walter Bright wrote:
> ```
> if (!a) a = b;
> ```
>
> Doesn't seem that bad. I did some searches and found hardly any 
> instances of it, though that was across the dmd sources.

I dont't know what regex have you used but here I've just tried 
`if( )+\(\![a-zA-Z_][a-zA-Z_0-9.]*\` and almost directly found an 
interesting example in typesem.d:

```d
Type referenceTo(Type type)
{
     if (type.ty == Terror)
         return type;
     if (!type.rto)
     {
         Type t = new TypeReference(type);
         type.rto = t.merge();
     }
     return type.rto;
}
```

could become

```d
Type referenceTo(Type type)
{
     if (type.ty == Terror)
         return type;
     return type.rto ?= new TypeReference(type).merge();
}
```

in particular here the opt-assign saves the double load on `type` 
to obtain `type.rto` as a lvalue.

More generally to the criticism that is "that does not seem very 
useful" I'd reply that at some point new language additions are 
necessarily "niches".