On 9 November 2013 00:15, Patrick Walton <pcwal...@mozilla.com> wrote:
> I don't see how you can without defeating separate compilation. If I am a
> function:
>
> fn f(s: ~str) {}
>
> It is `f`'s responsibility to free `s` at the end. That can't be done if
> this optimization has been performed.
This is about only optimizing fn f(t: &T) cases. Suppose one has a
custom 3-word struct with a destructor. Then with the current setup
one cannot hope that &T as a parameter would be just as efficient as
3-word ~str as the compiler uses an extra indirection. So the idea is
to say to the programmer: do not worry about this and always use &T as
a parameter type - the compiler will optimize it using the best mode
using internally pass-by-value if necessary.
With such optimization in place there would be no difference between
~str and struct MyStruct {s: ~str} as both ~str and &MyStruct as a
parameter generates exactly the same code.
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