Re: alias this and struct initializer

[Andre Pany via Digitalmars-d-learn]

On Thursday, 18 May 2017 at 12:56:09 UTC, Adam D. Ruppe wrote:

On Thursday, 18 May 2017 at 08:40:39 UTC, Andre Pany wrote:

[...]


Nope, case 2 is assigning to an already constructed object and 
case 3 is constructing a new one.


[...]


Thanks for the explanation, that makes perfectly sense.

Kind regards
André

Re: alias this and struct initializer

[Adam D. Ruppe via Digitalmars-d-learn]

On Thursday, 18 May 2017 at 08:40:39 UTC, Andre Pany wrote:

I think as case 2 is working case 3 should work also.


Nope, case 2 is assigning to an already constructed object and 
case 3 is constructing a new one.


alias this is NEVER used in construction. It can only apply after 
the object already exists, just like subclasses vs interfaces. 
Once the object exists, you can assign a subclass to an 
interface, but you can't do


SubClass obj = new Interface();

in theory, the compiler could see the left hand side and know it 
is supposed to be SubClass, but it doesn't - you need to 
construct the class explicitly.


Same with alias this, it allows implicit conversion TO the type 
and assignment of the member through the existing variable (the 
existing variable must already be valid, it is already 
constructed, so it is no different than assigning any other 
public member), but not implicit conversion FROM the type since 
the new struct may have other members that need to be initialized 
too.

alias this and struct initializer

[Andre Pany via Digitalmars-d-learn]

Hi,

I have some issues with struct initializer and alias this.
In following example 1 and 2 is working but there is a syntax
error for 3. I think as case 2 is working case 3 should work also.
For me case 3 is looking much nicer than case 1.
What do you think?

void main()
{
// Working
Request request1 = {
definitions: {[
Definition("A", "B")
]}
};

// Working
Request request2;
request2.definitions = [Definition()];

	// cannot implicitly convert expression ([Definition("A", "B")]) 
of type Definition[] to Definitions

Request request3 = {
definitions: [
Definition("A", "B")
]
};
}

struct Request
{
Definitions definitions;
}

struct Definitions
{
private Definition[] _arr;
alias values this;
@property Definition[] values(){return _arr;}
@property void values(Definition[] values){_arr = values;}
}

struct Definition
{
string attributeName;
string attributeType;
}

Kind regards
André