[Issue 21884] New: [betterC] can't compare arrays with -betterC

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21884

          Issue ID: 21884
           Summary: [betterC] can't compare arrays with -betterC
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: minor
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: blatblatnik at gmail.com

Without -betterC, the following code compiles:

bool fine() {
  float[2] a;
  return a == a;
}

It does exactly what you'd expect, and I'm happy. With -betterC however:

bool error() {
  float[2] a;
  return a == a; // Error: `TypeInfo` cannot be used with -betterC.
}

I don't know why dmd needs to emit type info for array comparisons. The type is
clearly known at compile time. I don't see why this wouldn't be possible in
-betterC.

By itself, this wouldn't be a massive issue, because we can also do

bool fine() {
  float[2] a;
  return a[] == a[];
}

And now this will compile and work as expected in -betterC. In fact I even
prefer this syntax personally since it's more consistent with other array
operations.

But this doesn't work for multi-dimensional arrays.

bool error() {
  float[2][2] a;
  return a == a;     // Error: `TypeInfo` cannot be used with -betterC.
  return a[] == a[]; // Error: `TypeInfo` cannot be used with -betterC.
}

And it definitely should work - at least one of these should work.

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