[Issue 12030] New: Detect some wrong array slice assignments at compile time

[d-bugmail at puremagic.com]

https://d.puremagic.com/issues/show_bug.cgi?id=12030

           Summary: Detect some wrong array slice assignments at compile
                    time
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: accepts-invalid
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody at puremagic.com
        ReportedBy: bearophile_hugs at eml.cc


--- Comment #0 from bearophile_hugs at eml.cc 2014-01-29 08:27:22 PST ---
This contains two related enhancement requests.

Some missed compile-time tests:

void main() {
    ubyte[10] a;
    ubyte[20] b;
    b[1 .. a.length + 2] = a[];
}


With dmd 2.065beta compiles with no errors and then gives at run-time:

object.Error: Array lengths don't match for copy: 10 != 11



void main() {
    int[10] a, b;
    b[$-5 .. $] = a[0 .. 4];
}


With dmd 2.065beta compiles with no errors and then gives at run-time:

object.Error: Array lengths don't match for copy: 4 != 5


I'd like those two programs to give compile-time errors. D is a statically
typed language, and I think there's there is enough compile-time information to
avoid errors at run-time.


Second enhancement request: once such tests are done at compile-time, there is
NO need to perform them again at run-time, speeding up the code a little.

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