Re: Why does struct initializer works for arrays but not for associative arrays?
On Wednesday, 14 March 2018 at 15:17:54 UTC, Jonathan M Davis
wrote:
On Wednesday, March 14, 2018 13:36:51 Andre Pany via
Digitalmars-d-learn wrote:
[...]
Well, I think that you have two issues here:
1. Struct literals work in only a few, specific circumstances.
Why, I don't know, but IIRC, someone was writing a DIP to fix
that, and that may or may not fix this case. So, as I
understand it, it's not all that hard to run into places where
they don't work (I confess that I never use them, because I
don't like them any more than I like the fact that struct
constructors are implicitly declared if you don't declare them,
which has caused me bugs when changing the members fo a struct;
both are misfeatures IMHO, though obviously not everyone agrees
on that point).
2. In general in D, the type of an expression is not inferred
based on where it's used. There are a few exceptions where
literals are involved, but in general, if you have something
like
A a = expression;
expression has to evaluate correct on its own without taking A
into account. The fact that something like
Bar b = {s: "str"};
compiles is actually a bit of an oddity in D's semantics in
that respect. So, the fact that it works at all is a bit of a
special case, and clearly, they didn't get everything. My guess
is that the problem is that the dynamic array literal needs a
type, but the compiler is not set up to figure out what type
that is based on the fact that it's being used in a struct
literal.
- Jonathan M Davis
Thanks for the information. As it works fine for dynamic arrays
and the coding
in the compiler seems identical for arrays and associative arrays
I really
wonder why it not work.
Although I really anticipate the DIP, this can be solved as bug
fix.
The chances to solve this a bug fix are much higher than getting
the DIP implemented
in near future (unfortunately).
Kind regards
André
Re: Why does struct initializer works for arrays but not for associative arrays?
On Wednesday, 14 March 2018 at 15:17:54 UTC, Jonathan M Davis wrote: On Wednesday, March 14, 2018 13:36:51 Andre Pany via Digitalmars-d-learn wrote: [...] Well, I think that you have two issues here: 1. Struct literals work in only a few, specific circumstances. Why, I don't know, but IIRC, someone was writing a DIP to fix that, and that may or may not fix this case. For reference, that's the DIP: https://github.com/dlang/DIPs/pull/71
Re: Why does struct initializer works for arrays but not for associative arrays?
On Wednesday, March 14, 2018 13:36:51 Andre Pany via Digitalmars-d-learn
wrote:
> Hi,
>
> I do not understand why struct initializer works for arrays but
> not for
> associative arrays:
>
> struct Bar
> {
> string s;
> }
>
> struct Foo
> {
> Bar[string] asso;
> Bar[] arr;
> }
>
> void main()
> {
> Foo foo = {
> arr: [{s: "123"}],
> asso: ["0": {s: "123"}] // does not work
> };
> }
>
> The coding for both types of arrays looks very similiar:
> https://github.com/dlang/dmd/blob/9ed779a7d68d2ac489338cc4758c10d0cb169b39
> /src/dmd/initsem.d#L634
>
> I cannot spot the difference.
>
> Kind regards
> André
Well, I think that you have two issues here:
1. Struct literals work in only a few, specific circumstances. Why, I don't
know, but IIRC, someone was writing a DIP to fix that, and that may or may
not fix this case. So, as I understand it, it's not all that hard to run
into places where they don't work (I confess that I never use them, because
I don't like them any more than I like the fact that struct constructors are
implicitly declared if you don't declare them, which has caused me bugs when
changing the members fo a struct; both are misfeatures IMHO, though
obviously not everyone agrees on that point).
2. In general in D, the type of an expression is not inferred based on where
it's used. There are a few exceptions where literals are involved, but in
general, if you have something like
A a = expression;
expression has to evaluate correct on its own without taking A into account.
The fact that something like
Bar b = {s: "str"};
compiles is actually a bit of an oddity in D's semantics in that respect.
So, the fact that it works at all is a bit of a special case, and clearly,
they didn't get everything. My guess is that the problem is that the dynamic
array literal needs a type, but the compiler is not set up to figure out
what type that is based on the fact that it's being used in a struct
literal.
- Jonathan M Davis
Re: Why does struct initializer works for arrays but not for associative arrays?
On Wednesday, 14 March 2018 at 13:36:51 UTC, Andre Pany wrote:
Hi,
I do not understand why struct initializer works for arrays but
not for
associative arrays:
struct Bar
{
string s;
}
struct Foo
{
Bar[string] asso;
Bar[] arr;
}
void main()
{
Foo foo = {
arr: [{s: "123"}],
asso: ["0": {s: "123"}] // does not work
};
}
The coding for both types of arrays looks very similiar:
https://github.com/dlang/dmd/blob/9ed779a7d68d2ac489338cc4758c10d0cb169b39/src/dmd/initsem.d#L634
I cannot spot the difference.
Kind regards
André
This might just be a bug. Changing the initializer to an explicit
call to Bar constructor compiles just fine
https://run.dlang.io/is/nuuolx
Even just doing
Foo foo = {
arr: [{s: "123"}],
asso: ["0": {"123"}] // does not work
};
Why does struct initializer works for arrays but not for associative arrays?
Hi,
I do not understand why struct initializer works for arrays but
not for
associative arrays:
struct Bar
{
string s;
}
struct Foo
{
Bar[string] asso;
Bar[] arr;
}
void main()
{
Foo foo = {
arr: [{s: "123"}],
asso: ["0": {s: "123"}] // does not work
};
}
The coding for both types of arrays looks very similiar:
https://github.com/dlang/dmd/blob/9ed779a7d68d2ac489338cc4758c10d0cb169b39/src/dmd/initsem.d#L634
I cannot spot the difference.
Kind regards
André
