On 03/10/2014 02:08 PM, Dicebot wrote:
On Sunday, 9 March 2014 at 21:31:40 UTC, Timon Gehr wrote:
http://wiki.dlang.org/DIP57/
Thoughts?
1)
Additionally, CTFE is invoked on all expressions occurring in the
ForeachAggregate
I think it can be phrased more universally "ForeachTypeList symbols must
be evaluated as compile-time entities, if it is not possible,
implementation-defined compilation error happens".
...
I don't see how this is more universal.
2) Saying that it does not introduce a new scope is not entirely true as
symbols from ForeachTypeList should not be available outside of static
foreach. You mention it later in the same block but it is important
concept to define as we currently don't have such pseudo-scopes
> ...
The description only says that the usual scope for foreach statements is
not introduced.
(do we?)
...
Nope.
3)
The body of the static foreach statement or static foreach declaration
is duplicated once for each iteration which the corresponding foreach
statement with an empty body would perform when executed in CTFE
I don't understand the reason behind limiting static foreach to CTFE
semantics. Simply evaluating and pasting the body for each iteration
should be enough. It is much closer to mixin template instances in that
regard.
...
I don't understand how the DIP is 'limiting static foreach to CTFE
semantics' and/or why this is a bad thing or how your suggestion is
different.
This will also remove necessity to rely on shadowing rules to re-define
ForeachTypeList symbols as at the time of pasting the body those won't
exist anymore.
...
I have no idea what this means.
4)
Declarations introduced in the body itself are inserted into this
enclosing scope
Isn't "enclosing" term used only for scope-to-scope relations or it is
applicable to any language construct? (I don't know)
...
There is no formal language spec. What is meant is the scope `hosting'
the static foreach construct.
5)
For static foreach statements, break and continue are supported and
treated like for foreach statements over tuples.
It is impossible as far as I understand existing semantics. Currently
placed continue/break refer to created scope and don't stop iteration
over remaining template argument list members. This is not applicable to
generic foreach.
...
This is not 'impossible', it is trivial to implement. Is your point that
you would prefer break and continue to affect static foreach expansion?
6)
In "Iterating over members of a scope" example there is a strange
Python-like colon after `static if` condition. Typo? :)
...
Nope. This is a language feature. See:
http://dlang.org/version.html
7)
In "Relation to tuple foreach" stating equivalency is not correct.
I have removed the section.
It is more of subset and even not a strict one as semantics will differ in
some corner cases.
I think as described they would not need to.
For example, iterating over expression list will
create a local copy right now if `ref` is not used. I'd really want this
to not be the case for static foreach.
...
I think the description is actually not detailed enough to warrant this
critique. (In particular, it is not clear what 'ref' should do.)
I.e., I think currently the following code is ambiguous:
int y,z;
static foreach(x;Seq!(y,z)) x = 2;
// what is the value of y and z now?
Overall provided examples seem to much my expectations but semantics
description can be more structured and detailed.
Agreed. I will do another iteration when I can find the time. Maybe I
will have to re-specify the behaviour of foreach though.
