Discussion Thread: DIP 1040--Copying, Moving, and Forwarding--Community Review Round 1
tsbockman
thomas.bockman at gmail.com
Fri Mar 5 23:03:57 UTC 2021
On Friday, 5 March 2021 at 12:19:54 UTC, Mike Parker wrote:
> This is the discussion thread for the first round of Community
> Review of DIP 1040, "Copying, Moving, and Forwarding":
From the DIP:
> A Move Constructor for struct S is declared as:
> this(S s) { ... }
> A Move Assignment Operator for struct S is declared as:
> void opAssign(S s) { ... }
Is the parameter to these methods really pass-by-value?
If so, why??? Making a copy during every move seems unnecessary,
and very inefficient. Moreover, for types that define a copy
constructor, it could reasonably be argued that calling it OR not
calling it BOTH violate the principle of least surprise. I expect
moves NOT to call the copy constructor, but I expect
pass-by-value WILL call it: a contradiction.
If the parameter is, in fact, intended to be pass-by-reference,
then I must strenuously object to the chosen syntax. Please do
not make this the one-and-only place in the entire language where
the pass-by-value syntax secretly means pass-by-reference. The
fact that `this(ref typeof(this))` is already taken by copy
constructors is NOT a good reason to violate the established
semantics of parameter lists in D. Just use a template parameter
to distinguish them, or something.
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