DIP 1016 should use expression lowering, not statement lowering

Steven Schveighoffer schveiguy at gmail.com
Thu Jan 31 02:29:47 UTC 2019

On 1/30/19 9:20 PM, Steven Schveighoffer wrote:

> Essentially, nothing is different from existing semantics today, when 
> rvalues are used and provides reference semantics (yes, it's possible, 
> see tempCString). They live until the end of the statement. It's how 
> this has to be. It can't be expression based.

I came up with this idea based on tempCString, but it doesn't work:

struct RV(T)
     T theThing;
     ref T getIt() { return theThing; }
     alias getIt this;

auto rv(T)(T t)
     import std.algorithm : move;
     return RV!T(move(t));

Of course, we'd need to suppress destructors here potentially.

I tried to use it:

import std.stdio;
void foo(ref int i) {writeln("i is ", i);}
void main()

But it fails:

Error: function testrvalue.foo(ref int i) is not callable using argument 
types (RV!int)
        cannot pass rvalue argument rv(1) of type RV!int to parameter 
ref int i

If I manually execute the alias this, it works:


So I don't get why it doesn't work. But if that was fixed, could be a 
potential workaround without requiring a DIP.


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