Is this really intended??

[claptrap]

On Sunday, 11 October 2020 at 18:57:55 UTC, Steven Schveighoffer 
wrote:
> On 10/10/20 8:16 PM, claptrap wrote:
>> struct Foo
>> {
>>      int i;
>>      void opAssign(int rhs) { this.i = rhs; }
>>      void reset() { i = 0; }
>> }
>> 
>> class Bar
>> {
>>      Foo foo;
>> 
>>      this()
>>      {
>>          foo.i = 0;    // *1
>>          foo.reset();  // *2
>>          foo = 42;
>>      }
>> }
>> 
>> With *1 & *2 commented out...
>> 
>> onlineapp.d(19): Error: cannot implicitly convert expression x 
>> of type int to Foo
>> onlineapp.d(19):        this.foo = x is the first assignment 
>> of this.foo therefore it represents its initialization
>> onlineapp.d(19):        opAssign methods are not used for 
>> initialization, but for subsequent assignments
>
> Hm.. yeah, this seems not right. The compiler should just go 
> ahead and initialize it if you try to call any methods on it 
> (including opAssign) before initialization.

I think the struct should be initialised full stop. I mean 
whether a member is initialised before the constructor is run 
shouldn't be dependent on what you do in the constructor. I mean 
you declare a struct, whether local or as part of an aggregate, 
it should be default initialised. Its a simple orthogonal rule.

If it's to do with being able to modify immutable members in the 
constructor that should be a separate rule. Either "You can 
modify immutable members in a constructor", or "you can construct 
immutable members in a constructor, but only once and it must be 
the first action on the member"

If there's a question of wasted effort initialising a member 
twice, the compiler should be able to elide the default 
initialiser, at least in simple cases the mechanism is already 
there.

They should be separate orthogonal rules.