Why exceptions for error handling is so important

[Walter Bright via Digitalmars-d]

On 1/13/2015 11:42 AM, "Marc =?UTF-8?B?U2Now7x0eiI=?= <schuetzm at gmx.net>" wrote:
> On Tuesday, 13 January 2015 at 00:05:31 UTC, Walter Bright wrote:
>> On 1/12/2015 3:17 PM, deadalnix wrote:
>>> On Monday, 12 January 2015 at 22:17:57 UTC, Walter Bright wrote:
>>>> Yes, it does. Returning an int in EAX now becomes returning a pair [EAX,EDX].
>>>
>>> It is not that big of a deal, EDX is a trash register anyway if memory serve,
>>> but then, it become very bad when it do not fit in register anymore.
>>
>> Returning a slice, for example, already consumes EAX and EDX. Adding an error
>> code pushes that into returning via a pointer to a stack temporary.
>>
>
> There are techniques to mitigate that. For example, Rust is smart enough to
> encode the "not-present" state for pointers as a NULL pointer (Rust pointers are
> non-null).

Such mitigation techniques pretty much confirms there's an efficiency cost to 
having the error code.

>
> If an error code needs to be returned, it can be encoded as a misaligned pointer
> (if you're feeling adventurous). Don't know whether Rust does the latter, though.
>
> Of course, these things have costs of their own.