Object.opEquals, opCmp, toHash

Timon Gehr timon.gehr at gmx.ch
Thu Feb 16 07:52:44 PST 2012

On 02/16/2012 09:35 AM, Walter Bright wrote:
> These all need to be:
> const pure nothrow @safe
> Unless this is done, the utility of const, pure, nothrow and @safe is
> rather crippled.
> Any reason why they shouldn't be?

The utility of const, pure, nothrow and @safe is already rather crippled 
when using Phobos. It is a rather small minority of my pure functions 
that are effectively annotated pure, because most of Phobos is not 
properly annotated and the inference for templates does not work 
satisfactorily yet.

So imo, making opEquals, opCmp, toHash const pure nothrow @safe is 
blocked by properly annotating Phobos as well as the following issues:

Bugs in existing attribute inference:

Enhancement required for making templates const correct:

> One reason is memoization, aka lazy initialization, aka logical const. I
> don't believe these are worth it. If you must do it inside those
> functions (and functions that override them), you're on your own to make
> it work right (use unsafe casts, etc.).

It would be helpful if we could add cast(pure) for that purpose. The 
documentation could state that cast(pure) is only valid if the behaviour 
of the enclosing function still appears to be pure.

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