🚀 go-pugleaf

In article 27354@mulga.cs.mu.OZ.AU, fjh@munta.cs.mu.OZ.AU (Fergus Henderson) writes:
>Michael Cook <mcook@cognex.com> writes:
>
>>>>>>> "SC" == Steve Clamage <clamage@Eng.sun.com> writes:
>>
>> SC> Silly example: Write a message to the terminal from the copy
>> SC> constructor. If the copy is optimized away, you won't see the message.
>>
>>If the constructor writes a message to the terminal, then the contructor has
>>side effects.  Such a constructor could not be optimized away and still
>>conform to the (drafts) standard, right?
>
>No, that's not right.  The draft standard explicitly gives implementations
>permission to optimize away copy constructors in this situation
>*even if they have side effects*.

Michael may have been thinking of the rule about unused variables. An
apparently unused variable must not be optimized away if its constructor
or destructor have side effects. (If they have no side effects, your
program couldn't tell whether the unused variable was created or destroyed
anyway.)

It is sometimes also necessary to point out the difference between copy
construction and copy assignment.
	// T is a type, and x is not type T
	T t1 = x; // may omit a temp T and avoid copying it
	T t2;
	t2 = x; // must create a temp T and assign it to t2
---
Steve Clamage, stephen.clamage@eng.sun.com



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