• d-bugmail puremagic.com (36/36) Sep 25 2023 https://issues.dlang.org/show_bug.cgi?id=24159

d-bugmail puremagic.com writes:

https://issues.dlang.org/show_bug.cgi?id=24159

          Issue ID: 24159
           Summary: BetterC: appending to dynamic arrays no longer errors
                    at compile time
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Keywords: betterC
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody puremagic.com
          Reporter: dave287091 gmail.com

The following program compiled with betterC used to error at compile time, now
it only errors at runtime:

extern(C)
int main(){
    int[] x = null;
    x ~= 3; // this should be diagnosed at compile time
    return x[0];
}

You now get a runtime assertion like:

Assertion failed: (Cannot append to array if compiling without support for
runtime type information!), function
core.internal.array.appending._d_arrayappendcTXImpl!(int[],
int)._d_arrayappendcTX, file <snip>/import/core/internal/array/appending.d,
line 52.

Which is this file:
https://github.com/dlang/dmd/blob/396fc8d477ca66e20f6b4fec4d532f2aee053ba3/druntime/src/core/internal/array/appending.d#L52

Getting an error at runtime is much worse than compile time as some code might
be rarely exercised.

Also note that the failed assertion doesn’t even point to your line of code
where you used a feature banned in betterC!

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