Cannot compare object.opEquals is not nogc

[lqjglkqjsg via Digitalmars-d-learn]

On Sunday, 24 July 2016 at 15:09:53 UTC, Lodovico Giaretta wrote:
> Yes, making them @nogc would require all existing overrides to 
> be changed (overrides cannot throw away attributes, but must 
> specify them explicitly as in the parent class, or stricter).
> The real problem making these @nogc is that with the current 
> state of things @nogc implies nothrow, thus preventing 
> exceptions (of course we should work to change this thing, and 
> I'm personally researching convenient ways of doing it; I'll 
> soon write a post on General about this).
>
> Remember that comparison of complex objects may require 
> normalization, which may change the objects themselves and 
> allocate memory. Also, comparisons may throw exceptions that 
> need the GC (see above). So I'm personally against making those 
> methods @nogc.
>
> But I'm also against a singly-rooted hierarchy. Removing Object 
> and having multiple class hierarchies would entirely solve the 
> issue. But please note that you can already "do" that: if you 
> never use Object, but always subclasses, the fact that Object 
> isn't @nogc is no longer an issue. While Object (if it exists) 
> must support any kind of descendant (and thus cannot pose 
> arbitrary limitations like @nogc is), the roots of 
> domain-specific hierarchies can exploit the fact that they are 
> domain-specific to impose meaningful limitations, based on the 
> expected usage and behaviour, and can thus be @nogc. And you 
> can either limit your algorithm inputs to objects of a specific 
> hierarchy or, if you want it generic, use a template (read as: 
> you don't use Object explicitly, as if it doesn't exists).

Almost off topic but I've recognized a typical error here, I 
think that many of us have already seen it too. You develop a 
nice class. You put attributes everywhere @safe pure nothrow 
@nogc. Yay the unittest pass.

Later you use it for real and you realize then that the 
attributes must be removed because you can't do anything in the 
overriden methods.