Hi,

I am really confused, why is this valid:
void sample(string[string] s = string[string].init){}

while this causes syntax errors?

void sample_invalid1(double[string] s = double[string].init){}
void sample_invalid2(int[int] s = int[int].init){}

Kind regards
André

On Tuesday, 22 December 2020 at 21:11:12 UTC, Andre Pany wrote:
> I am really confused, why is this valid:
> void sample(string[string] s = string[string].init){}
>
> while this causes syntax errors?
>
> void sample_invalid1(double[string] s = double[string].init){}
> void sample_invalid2(int[int] s = int[int].init){}

Looks like an oddity in the grammar.

`string` is an alias, meaning it's an identifier. And an identifier is a valid expression to the grammar. So `string[string]` is parsed as an IndexExpression. Only during semantic analysis does the compiler figure out that it's actually a type.

`double` and `int` aren't identifiers. They're keywords. And they're always types, never expressions. So `int[int]` cannot be parsed as an IndexExpression. It's parsed as a Type instead. And for a (grammatical) Type, there is no rule that allows `Type.Identifier`.

You can work around with parentheses:

(double[string]).init;
(int[int]).init

On Tuesday, 22 December 2020 at 22:02:54 UTC, ag0aep6g wrote:
> On Tuesday, 22 December 2020 at 21:11:12 UTC, Andre Pany wrote:
>> [...]
>
> Looks like an oddity in the grammar.
>
> `string` is an alias, meaning it's an identifier. And an identifier is a valid expression to the grammar. So `string[string]` is parsed as an IndexExpression. Only during semantic analysis does the compiler figure out that it's actually a type.
>
> `double` and `int` aren't identifiers. They're keywords. And they're always types, never expressions. So `int[int]` cannot be parsed as an IndexExpression. It's parsed as a Type instead. And for a (grammatical) Type, there is no rule that allows `Type.Identifier`.
>
> You can work around with parentheses:
>
> (double[string]).init;
> (int[int]).init

Thanks a lot!

Kind regards
Andre

On Tue, Dec 22, 2020 at 10:15 PM Andre Pany via Digitalmars-d-learn < digitalmars-d-learn@puremagic.com> wrote:

> Hi,
>
> I am really confused, why is this valid:
> void sample(string[string] s = string[string].init){}
>
> while this causes syntax errors?
>
> void sample_invalid1(double[string] s = double[string].init){}
> void sample_invalid2(int[int] s = int[int].init){}
>
> Kind regards
> André
>

As has been said this is an oddity in the grammar. But why would anyone need to use this anyway?

  void sample_invalid2(int[int] s = int[int].init){}

seems really awful to me anyway.

On 12/22/20 5:44 PM, Daniel Kozak wrote:
> On Tue, Dec 22, 2020 at 10:15 PM Andre Pany via Digitalmars-d-learn <digitalmars-d-learn@puremagic.com <mailto:digitalmars-d-learn@puremagic.com>> wrote:
> 
>     Hi,
> 
>     I am really confused, why is this valid:
>     void sample(string[string] s = string[string].init){}
> 
>     while this causes syntax errors?
> 
>     void sample_invalid1(double[string] s = double[string].init){}
>     void sample_invalid2(int[int] s = int[int].init){}
> 
>     Kind regards
>     André
> 
> 
> As has been said this is an oddity in the grammar. But why would anyone need to use this anyway?
> 
>    void sample_invalid2(int[int] s = int[int].init){}
> 
> seems really awful to me anyway.

Yeah:

void sample_valid(int[int] s = null)

-Steve

Dne st 23. 12. 2020 1:00 uživatel Steven Schveighoffer via Digitalmars-d-learn <digitalmars-d-learn@puremagic.com> napsal:

> On 12/22/20 5:44 PM, Daniel Kozak wrote:
> > On Tue, Dec 22, 2020 at 10:15 PM Andre Pany via Digitalmars-d-learn <digitalmars-d-learn@puremagic.com <mailto:digitalmars-d-learn@puremagic.com>> wrote:
> >
> >     Hi,
> >
> >     I am really confused, why is this valid:
> >     void sample(string[string] s = string[string].init){}
> >
> >     while this causes syntax errors?
> >
> >     void sample_invalid1(double[string] s = double[string].init){}
> >     void sample_invalid2(int[int] s = int[int].init){}
> >
> >     Kind regards
> >     André
> >
> >
> > As has been said this is an oddity in the grammar. But why would anyone need to use this anyway?
> >
> >    void sample_invalid2(int[int] s = int[int].init){}
> >
> > seems really awful to me anyway.
>
> Yeah:
>
> void sample_valid(int[int] s = null)
>
> -Steve


Yes AA.init is null per doc.

https://dlang.org/spec/hash-map.html#construction_and_ref_semantic

On Wednesday, 23 December 2020 at 07:08:31 UTC, Daniel Kozak wrote:
> Dne st 23. 12. 2020 1:00 uživatel Steven Schveighoffer via Digitalmars-d-learn <digitalmars-d-learn@puremagic.com> napsal:
>
>> On 12/22/20 5:44 PM, Daniel Kozak wrote:
>> > [...]
>>
>> Yeah:
>>
>> void sample_valid(int[int] s = null)
>>
>> -Steve
>
>
> Yes AA.init is null per doc.
>
> https://dlang.org/spec/hash-map.html#construction_and_ref_semantic

Thanks for clarification, I was not aware that AA.init is technically the same as null.

Kind regards
Andre