https://issues.dlang.org/show_bug.cgi?id=17245

          Issue ID: 17245
           Summary: Errors about expressions with no effect only are given
                    for basic types
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody@puremagic.com
          Reporter: jack@jackstouffer.com

Example

void main () {
    Object a, b;
    a == b;
}

gives no error.

The problem lies, as ketmar put it, with opEquals

> oops. no more error messages. yes, i know that this invokes `opEquals()`, and `opEquals()` can have side-effects. but what are the chances of writing such code *intentionally*?

Here, the compiler can be helpful by outputing an error if the used opEquals is marked as pure. There's no way that a pure opEquals should be used in an expression with no effect.

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