• Andrey Zherikov (18/18) Sep 18 2020 How can I rewrite foo() function as a free-function that won't
• H. S. Teoh (6/24) Sep 18 2020 Why can't you return by ref, which would also avoid the copying?
• Andrey Zherikov (6/8) Sep 18 2020 Compiler errors out:
• Andrey Zherikov (37/39) Sep 18 2020 I found solution:

Andrey Zherikov <andrey.zherikov gmail.com> writes:

How can I rewrite foo() function as a free-function that won't 
cause struct copying? My simplified code is:
========
struct S
{
     ref S foo() return
     {
         return this;
     }
}

void main()
{
     S().foo().foo().foo();
}
========
If I write it like "auto foo(S s) { return s; }" then statement 
in main() will copy value of S three times and I want to avoid 
this.

"H. S. Teoh" <hsteoh quickfur.ath.cx> writes:

On Fri, Sep 18, 2020 at 06:20:41PM +0000, Andrey Zherikov via
Digitalmars-d-learn wrote:
 How can I rewrite foo() function as a free-function that won't cause
 struct copying? My simplified code is:
 ========
 struct S
 {
     ref S foo() return
     {
         return this;
     }
 }
 
 void main()
 {
     S().foo().foo().foo();
 }
 ========
 If I write it like "auto foo(S s) { return s; }" then statement in
 main() will copy value of S three times and I want to avoid this.

Why can't you return by ref, which would also avoid the copying?

	ref S foo(return ref S s) { return s; }


T

-- 
Let's not fight disease by killing the patient. -- Sean 'Shaleh' Perry

Andrey Zherikov <andrey.zherikov gmail.com> writes:

On Friday, 18 September 2020 at 18:43:38 UTC, H. S. Teoh wrote:
 Why can't you return by ref, which would also avoid the copying?

 	ref S foo(return ref S s) { return s; }

Compiler errors out:
onlineapp.d(9): Error: function onlineapp.foo(return ref S s) is 
not callable using argument types (S)
onlineapp.d(9):        cannot pass rvalue argument S() of type S 
to parameter return ref S s

Andrey Zherikov <andrey.zherikov gmail.com> writes:

On Friday, 18 September 2020 at 18:20:41 UTC, Andrey Zherikov 
wrote:
 How can I rewrite foo() function as a free-function that won't 
 cause struct copying?

I found solution:
========
struct S
{
     int i = -1;
     this(int n) {i=n;writeln(&this," ",i," 
",__PRETTY_FUNCTION__);}
     this(ref return scope inout S rhs) inout 
{i=rhs.i+1;writeln(&this," ",i," ",__PRETTY_FUNCTION__);}
     ~this() {writeln(&this," ",i," ",__PRETTY_FUNCTION__);}
     ref auto getRef() return
     {
	    writeln(&this," ",i," ",__PRETTY_FUNCTION__);
         return this;
     }
}

ref auto foo(return ref S s)
{
     writeln(&s," ",s.i," ",__PRETTY_FUNCTION__);
     return s;
}

void main()
{
     S(5).getRef().foo().foo().foo();
}
========

Output confirms that there is no copying happens:
========
7FFDE98BDDF0 5 S onlineapp.S.this(int n) ref
7FFDE98BDDF0 5 onlineapp.S.getRef() ref return
7FFDE98BDDF0 5 onlineapp.foo(return ref S s) ref  system
7FFDE98BDDF0 5 onlineapp.foo(return ref S s) ref  system
7FFDE98BDDF0 5 onlineapp.foo(return ref S s) ref  system
7FFDE98BDDF0 5 void onlineapp.S.~this()
========