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digitalmars.D.bugs - [Issue 8845] New: Can't pass immediate or rvalue args to ref function parameters

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8845

           Summary: Can't pass immediate or rvalue args to ref function
                    parameters
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: turkeyman gmail.com



Consider:
float length(ref const(Vector) x);

float distBetween = length(p1 - p0);
 or
float speed = length(player.getVelocity());

These don't work, forcing this horrible code:

Vector diff = p0 - p1;
float distBetween = length(diff);

Naturally, if I have a series of these operations, I end up with:

Vector diff0 = p0 - p1;
Vector diff1 = p1 - p2;
Vector diff2 = p2 - p0;

And it all starts getting very silly, the local namespace gets polluted very
quickly, and sensible temporary names often don't even exist for these
intermediate concepts, leading to really stupid names, or just random letters.

There's no difference in security. Forcing creation of a function scoped
variable just increases the probability of name conflict and inconveniences the
programmer. It would be nicer if the temporary was only scoped for life within
the functions call, and also un-named, so it doesn't pollute the functions
namespace.

I've heard arguments about the safety of the operation, but the 'workaround' is
just to create a temporary, which has identical security properties. It's also
no different than passing any pointer normally (a common suggestion), and no
reason to significantly inconvenience the programmer.

Perhaps this behaviour could be restricted to ref const, or ref in, if we're
getting worried about the safety of the operation? That would perhaps even
improve on how behaves now.

This is particularly common when working with linear algebra. Vectors,
matrices, quaternions are surely the most likely to produce this pattern.

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parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8845


bearophile_hugs eml.cc changed:

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 This is particularly common when working with linear algebra. Vectors,
 matrices, quaternions are surely the most likely to produce this pattern.


Yes, it's a common pattern (Example: I have seen it often in a little
ray-tracer).

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