int[int] hash;

..

foreach( key, ref value; hash ) {
	if( value>12 )
		hash.remove(key);
}

Some hash implementations support this, some don't. The D documentation (https://dlang.org/spec/hash-map.html) leaves this not defined.

As reference, C++ does define this (in C++ it is allowed, at least since C++14: http://en.cppreference.com/w/cpp/container/unordered_map/erase)

Shachar

On 11/02/2016 10:21 AM, Shachar Shemesh wrote:
> int[int] hash;
>
> ..
>
> foreach( key, ref value; hash ) {
>     if( value>12 )
>         hash.remove(key);
> }
>
> Some hash implementations support this, some don't. The D documentation
> (https://dlang.org/spec/hash-map.html) leaves this not defined.
>
> As reference, C++ does define this (in C++ it is allowed, at least since
> C++14: http://en.cppreference.com/w/cpp/container/unordered_map/erase)
>
> Shachar

We should render it defined, and document it as such. Could you please create an issue and I'll have someone look at it. Thanks! -- Andrei

On Wednesday, 2 November 2016 at 14:21:32 UTC, Shachar Shemesh wrote:
> The D documentation (https://dlang.org/spec/hash-map.html) leaves this not defined.

The foreach statement is defined to not allow it:

http://dlang.org/spec/statement.html#ForeachStatement

"The aggregate must be loop invariant, meaning that elements to the aggregate cannot be added or removed from it in the NoScopeNonEmptyStatement."

On 11/02/2016 11:17 AM, Adam D. Ruppe wrote:
> On Wednesday, 2 November 2016 at 14:21:32 UTC, Shachar Shemesh wrote:
>> The D documentation (https://dlang.org/spec/hash-map.html) leaves this
>> not defined.
>
> The foreach statement is defined to not allow it:
>
> http://dlang.org/spec/statement.html#ForeachStatement
>
> "The aggregate must be loop invariant, meaning that elements to the
> aggregate cannot be added or removed from it in the
> NoScopeNonEmptyStatement."

Yah, we'd do good to relax that to allow removal of the currently iterated element. -- Andrei

On 02/11/16 16:52, Andrei Alexandrescu wrote:
> We should render it defined, and document it as such. Could you please
> create an issue and I'll have someone look at it. Thanks! -- Andrei

https://issues.dlang.org/show_bug.cgi?id=16659

On 11/2/16 11:17 AM, Adam D. Ruppe wrote:
> On Wednesday, 2 November 2016 at 14:21:32 UTC, Shachar Shemesh wrote:
>> The D documentation (https://dlang.org/spec/hash-map.html) leaves this
>> not defined.
>
> The foreach statement is defined to not allow it:
>
> http://dlang.org/spec/statement.html#ForeachStatement
>
> "The aggregate must be loop invariant, meaning that elements to the
> aggregate cannot be added or removed from it in the
> NoScopeNonEmptyStatement."

That's only for builtins. Obviously, there are cases where it can work, and it needs to be defined by the aggregate/range. I think the documentation should be updated to reflect that.

To answer the original question, it's not valid with the current implementation AFAIK. I don't think we should define ever that it is valid, even if we have an implementation that supports it, as this restricts our implementation to always supporting it.

I'll point at my dcollections library as an example where the currently iterated value can be removed:

https://github.com/schveiguy/dcollections/blob/master/concepts.txt#L81

I think Java also allows this, and C++ allows this.

-Steve