Hello. Please see the following code:

import std.stdio ;
struct Pair {
	int x, y ;
	this (int x, int y) { x = x ; y = y ; }
}
void main() {
	auto P = Pair(1, 2) ;
	writeln(P.x, ' ', P.y) ;
}

This outputs 0 0, whereas the equivalent C++ code outputs 1 2 correctly:

# include <iostream>
struct Pair {
	int x, y ;
	Pair(int x, int y) : x(x), y(y) {}
} ;
int main() {
	auto P = Pair(1, 2) ;
	std::cout << P.x << ' ' << P.y << std::endl ;
}

It seems to me that D should either not permit argument names to shadow the member names, since it has no initializer lists and all members are automatically initialized. Comments?

-- 
Shriramana Sharma ஶ்ரீரமணஶர்மா श्रीरमणशर्मा

On 10/23/14 1:03 AM, Shriramana Sharma via Digitalmars-d-learn wrote:
> Hello. Please see the following code:
>
> import std.stdio ;
> struct Pair {
> 	int x, y ;
> 	this (int x, int y) { x = x ; y = y ; }
> }
> void main() {
> 	auto P = Pair(1, 2) ;
> 	writeln(P.x, ' ', P.y) ;
> }
>
> This outputs 0 0, whereas the equivalent C++ code outputs 1 2 correctly:
>
> # include <iostream>
> struct Pair {
> 	int x, y ;
> 	Pair(int x, int y) : x(x), y(y) {}
> } ;

This is not the same. In the above, the x outside the parens is ALWAYS a member. D does not have this syntax. Change it to the same as your D implementation, and you get the same result (actually worse, because C++ will not initialize x and y for you).

> int main() {
> 	auto P = Pair(1, 2) ;
> 	std::cout << P.x << ' ' << P.y << std::endl ;
> }
>
> It seems to me that D should either not permit argument names to
> shadow the member names, since it has no initializer lists and all
> members are automatically initialized. Comments?

You're missing the "or" part of that statement :)

But 2 things:

x = x;

This should produce an error, or at least a warning I think, as it does nothing. However, even with dmd -w, it does not. I know I have seen the compiler complain about noop statements before, I just don't know under what circumstances

and 2, you would use the same mechanism as you use with C++ to initialize the items inside the ctor:

this.x = x;

Note, the rules for shadowing are the same as for any function parameters to any function vs. members or module variables. Nothing is inconsistent here.

-Steve