Re: Struct Constructor Lazy

[Biotronic via Digitalmars-d-learn]

On Wednesday, 12 July 2017 at 11:00:54 UTC, Jiyan wrote:
Hey there:)
i want to know whether the following is somehow possible:
structs dont have default constructors, i know so:

struct A
{
int field;
this(int i){field = getDataFromFile("file.txt");}
}

A instance = A(0);

Here comes my issue:
when A(0) is called I would want here optimal performance, so 
there doesnt even need to be a value pushed on the stack (i=0), 
what would be like having a constructor with zero arguments (i 
is never used!).
Im pretty new to D, can somebody tell me how i would do this?
Is this(lazy int i){ ... a solution?

The traditional solution is static opCall:

struct A {
    int field;
    static A opCall() {
        A result;
        result.field = getDataFromFile("file.txt");
        return result;
    }
}

A instance = A();

I believe I've heard this is frowned upon these days, but I don't 
know of a better solution.

For optimal speed you might also want to skip default 
initialization of result, by writing A result = void;.

I would be surprised if the optimizer wasn't able to optimize 
away the useless parameter though - have you looked at the 
generated assembly?

--
  Biotronic