study: use checkedint as a drop-in replacement of native long
mingwu at gmail.com
Mon Aug 17 20:53:31 UTC 2020
On Monday, 17 August 2020 at 18:10:16 UTC, H. S. Teoh wrote:
> On Mon, Aug 17, 2020 at 05:58:16PM +0000, mw via Digitalmars-d
>> On Monday, 17 August 2020 at 17:15:59 UTC, H. S. Teoh wrote:
>> > Chain assignment fix:
>> > https://github.com/dlang/phobos/pull/7599
>> Thanks for the PR, I just added comments: does this fix also
>> work for mixed native & checked chain assignment? i.e. add to
>> long la, lb;
>> Checked!long ca, cb;
>> la = ca = lb = cb; // mixed chain assign
>> ca = la = cb = lb;
> Currently, it doesn't work. I'm on the fence about whether it
> should: the whole point of using Checked is that you don't want
> to automatically convert to the native type because the
> converted value will lose the protections conferred by Check.
> Assigning a Checked to a native type *might* be a mistake - you
> thought the variable was Checked but it wasn't, so subsequent
> operations on it no longer has Checked semantics even though
Yes, that's the principle we all agree. However, we are talking
about opAssign() here.
The user specifies his/her intention via the variable's type
declaration, e.g. native `long` vs checked `Long`. The
*subsequent* operations you talking about will be on user
specified variable (type), there will be no surprise here: if the
LHS is declared as a `long`, the subsequent operations will be on
`long`, and if the LHS is `Long`, the subsequent operations will
be on `Long`, all as user has specified.
opAssign() just make the boxing/unboxing life easier between
these two types. And there is not any mathematical operation
performed inside opAssign(), hence for this particular function,
native == checked is always true. So I think let opAssign()
return the underlying type will make the drop-in replacement
process more smooth, and without extra correctness concern.
> you thought it does. So I'm not sure this case should be
> supported. Assigning from Checked back to native should always
> be explicit IMO (the programmer explicitly indicates he doesn't
> want Checked protections anymore).
More information about the Digitalmars-d