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September 18, 2020 How to convert member function to free function? | ||||
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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. |
September 18, 2020 Re: How to convert member function to free function? | ||||
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Posted in reply to Andrey Zherikov | 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 |
September 18, 2020 Re: How to convert member function to free function? | ||||
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Posted in reply to H. S. Teoh | 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
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September 18, 2020 Re: How to convert member function to free function? | ||||
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Posted in reply to Andrey Zherikov | 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() ======== |
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