Just for fun I decided to complete some codejam challenges in D. At some point I wanted to add structs to an array but I got a compiler error. What am I doing wrong?

code:
struct test{
int x;
int y;
}
void main(){
test[] why;
why~={3,5};
}

error:
wait.d(7): found '}' when expecting ';' following statement
wait.d(8): found 'EOF' when expecting ';' following statement
wait.d(8): found 'EOF' when expecting '}' following compound statement

Is there any reason a why this wouldn't work?

On Tue, 17 Apr 2012 22:28:31 +0200, maarten van damme <maartenvd1994@gmail.com> wrote:

> Just for fun I decided to complete some codejam challenges in D. At some
> point I wanted to add structs to an array but I got a compiler error. What
> am I doing wrong?
>
> code:
> struct test{
> int x;
> int y;
> }
> void main(){
> test[] why;
> why~={3,5};
> }
>
> error:
> wait.d(7): found '}' when expecting ';' following statement
> wait.d(8): found 'EOF' when expecting ';' following statement
> wait.d(8): found 'EOF' when expecting '}' following compound statement
>
> Is there any reason a why this wouldn't work?

Sounds like a bug. C style initializers work in other cases:

struct S { int i; }
void main() {
    S[] arr;
    S s = { 1 };
    arr ~= S(1);
    // But the following barfs
    //arr ~= { 1 };
    //arr ~= { i:1 };
    //arr[0] = { 1 };
}

simendsjo:

> Sounds like a bug. C style initializers work in other cases:

D language is so much irregular, so many special cases that don't work :-)

Bye,
bearophile

On Tuesday, 17 April 2012 at 21:00:55 UTC, simendsjo wrote:
> On Tue, 17 Apr 2012 22:28:31 +0200, maarten van damme <maartenvd1994@gmail.com> wrote:
>
>> Just for fun I decided to complete some codejam challenges in D. At some
>> point I wanted to add structs to an array but I got a compiler error. What
>> am I doing wrong?
>>
>> code:
>> struct test{
>> int x;
>> int y;
>> }
>> void main(){
>> test[] why;
>> why~={3,5};
>> }
>>
>> error:
>> wait.d(7): found '}' when expecting ';' following statement
>> wait.d(8): found 'EOF' when expecting ';' following statement
>> wait.d(8): found 'EOF' when expecting '}' following compound statement
>>
>> Is there any reason a why this wouldn't work?
>
> Sounds like a bug. C style initializers work in other cases:
>
> struct S { int i; }
> void main() {
>     S[] arr;
>     S s = { 1 };
>     arr ~= S(1);
>     // But the following barfs
>     //arr ~= { 1 };
>     //arr ~= { i:1 };
>     //arr[0] = { 1 };
> }

No, it is designed. {3,5} is struct initializer:
http://dlang.org/declaration.html#StructInitializer
And it is only allowed in initializer of variable declarations.

> why~={3,5};

This is concat assign expression, so you should use test(3,5)
instead of {3,5}. That is StructLiteral:
http://dlang.org/struct.html#StructLiteral
and it is an expression.

Bye.

Kenji Hara

On 04/17/2012 02:00 PM, simendsjo wrote:

> Sounds like a bug. C style initializers work in other cases:

I try not to use them. I think they have this 'feature' of leaving unspecified members uninitialized:

struct S
{
    int i;
    double d;
}

void main()
{
    S s = { 42 };               // <-- no initializer for S.d
    assert(s.i == 42);
    assert(s.d == double.nan);  // <-- fails (may work for you)
}

Is that a bug or a feature? I might have opened it but I don't remember now. :)

Ali

On Wednesday, 18 April 2012 at 04:55:23 UTC, Ali Çehreli wrote:
> On 04/17/2012 02:00 PM, simendsjo wrote:
>
> > Sounds like a bug. C style initializers work in other cases:
>
> I try not to use them. I think they have this 'feature' of leaving unspecified members uninitialized:
>
> struct S
> {
>     int i;
>     double d;
> }
>
> void main()
> {
>     S s = { 42 };               // <-- no initializer for S.d
>     assert(s.i == 42);
>     assert(s.d == double.nan);  // <-- fails (may work for you)

You should use std.math.isNaN whether a floating point value is NaN.

      assert(isNaN(s.d));  // <-- success

> }
>
> Is that a bug or a feature? I might have opened it but I don't remember now. :)
>
> Ali

Bye.

Kenji Hara

That's a very odd design. Making it work when instantiating a new struct of that type but not inline. Anyway, test(3,5) works perfect, thank you.

Le 18/04/2012 12:41, maarten van damme a écrit :
> That's a very odd design. Making it work when instantiating a new struct of that type but not inline. Anyway, test(3,5) works perfect, thank you.

It's not odd at all. You append a structure, not an array.
{3,5} is for array initialization, it's the same syntax as in C, C++,
Java, C#.

What if you want to append an array of structures ?

    why~=[test(3,5), test(3,6)];

On 04/18/2012 12:16 AM, Kenji Hara wrote:
> On Wednesday, 18 April 2012 at 04:55:23 UTC, Ali Çehreli wrote:

>> assert(s.d == double.nan); // <-- fails (may work for you)
>
> You should use std.math.isNaN whether a floating point value is NaN.
>
> assert(isNaN(s.d)); // <-- success

That a thousandth time I have made that mistake and still have not learned. :( Yes, .nan may not be compared with any other value, including .nan.

Ali

Ali:
> That a thousandth time I have made that mistake and still have not learned. :( Yes, .nan may not be compared with any other value, including .nan.

Today I'll present an enhancement request to remove this problem from D.

Hugs,
bearophile