digitalmars.D.learn - Is it possible to modify shared struct array in a function.

Sudhi (40/40) Feb 07 2019 I have a situation, where i want to modify a shared variable in a

Arun Chandrasekaran (3/43) Feb 07 2019 Works fine for me with DMD64 D Compiler v2.083.1.

Sudhi (39/93) Feb 07 2019 My example code was wrong. Below is the right one.

Arun Chandrasekaran (3/43) Feb 07 2019 `shared struct Metadata` should make it work.
Jerry (7/51) Feb 07 2019 You have to cast away shared:

Eduard Staniloiu (30/91) Feb 08 2019 You do not need to cast away shared. You had a couple of issues

Jonathan M Davis (10/116) Feb 08 2019 Honestly, the fact that that code compiles is a bug. You're not supposed...

Sudhi <sudheendra.malli gmail.com> writes:

I have a situation, where i want to modify a shared variable in a 
function. Something like below

struct Company
{
     string name;
     string location;
}

struct Racks
{
     int number;
     int location;
}

struct Metadata
{
     string name;
     Company[] companies;
     Racks[] racks;
}

struct Item
{
     Metadata met;
     int count;
}

shared (Item) item

void main()
{
    updateMetadata()
}

void updateMetadata()
{
    Company company;
    company.name = "Hello";
    company.location = "Bangalore";
    item.met.companies ~= company;
}

Compiler throws me error in last line for appending as below.

"cannot append type Metadata to type shared(Metadata[])".

Please let me know if there is a way to acheive this.

Thanks,
Sudhi

Feb 07 2019

Arun Chandrasekaran <aruncxy gmail.com> writes:

On Friday, 8 February 2019 at 04:13:39 UTC, Sudhi wrote:
 I have a situation, where i want to modify a shared variable in 
 a function. Something like below

 struct Company
 {
     string name;
     string location;
 }

 struct Racks
 {
     int number;
     int location;
 }

 struct Metadata
 {
     string name;
     Company[] companies;
     Racks[] racks;
 }

 struct Item
 {
     Metadata met;
     int count;
 }

 shared (Item) item

 void main()
 {
    updateMetadata()
 }

 void updateMetadata()
 {
    Company company;
    company.name = "Hello";
    company.location = "Bangalore";
    item.met.companies ~= company;
 }

 Compiler throws me error in last line for appending as below.

 "cannot append type Metadata to type shared(Metadata[])".

 Please let me know if there is a way to acheive this.

 Thanks,
 Sudhi

Works fine for me with DMD64 D Compiler v2.083.1. 
https://run.dlang.io/is/RRM8GU

Feb 07 2019

Sudhi <sudheendra.malli gmail.com> writes:

On Friday, 8 February 2019 at 04:30:23 UTC, Arun Chandrasekaran 
wrote:
 On Friday, 8 February 2019 at 04:13:39 UTC, Sudhi wrote:
 I have a situation, where i want to modify a shared variable 
 in a function. Something like below

 struct Company
 {
     string name;
     string location;
 }

 struct Racks
 {
     int number;
     int location;
 }

 struct Metadata
 {
     string name;
     Company[] companies;
     Racks[] racks;
 }

 struct Item
 {
     Metadata met;
     int count;
 }

 shared (Item) item

 void main()
 {
    updateMetadata()
 }

 void updateMetadata()
 {
    Company company;
    company.name = "Hello";
    company.location = "Bangalore";
    item.met.companies ~= company;
 }

 Compiler throws me error in last line for appending as below.

 "cannot append type Metadata to type shared(Metadata[])".

 Please let me know if there is a way to acheive this.

 Thanks,
 Sudhi

 Works fine for me with DMD64 D Compiler v2.083.1. 
 https://run.dlang.io/is/RRM8GU


My example code was wrong. Below is the right one.

struct Company
{
     string name;
     string location;
}

struct Racks
{
     int number;
     int location;
}

struct Metadata
{
     string name;
     Company[] companies;
     Racks[] racks;
}

struct Item
{
     Metadata[] met;
     int count;
}

shared (Item) item;

void main()
{
    updateMetadata();
}

void updateMetadata()
{
    Company company;
    company.name = "Hello";
    company.location = "Bangalore";
    item.met.companies ~= company;
    import std.stdio: writeln;
    writeln(item);
}

https://run.dlang.io/is/iem0PY

Feb 07 2019

Arun Chandrasekaran <aruncxy gmail.com> writes:

On Friday, 8 February 2019 at 04:51:08 UTC, Sudhi wrote:
 On Friday, 8 February 2019 at 04:30:23 UTC, Arun Chandrasekaran 
 wrote:
 [...]


 My example code was wrong. Below is the right one.

 struct Company
 {
     string name;
     string location;
 }

 struct Racks
 {
     int number;
     int location;
 }

 struct Metadata
 {
     string name;
     Company[] companies;
     Racks[] racks;
 }

 struct Item
 {
     Metadata[] met;
     int count;
 }

 shared (Item) item;

 void main()
 {
    updateMetadata();
 }

 void updateMetadata()
 {
    Company company;
    company.name = "Hello";
    company.location = "Bangalore";
    item.met.companies ~= company;
    import std.stdio: writeln;
    writeln(item);
 }

 https://run.dlang.io/is/iem0PY

`shared struct Metadata` should make it work.

Turtles (shared) all the way down.

Feb 07 2019

Jerry <labuurii gmail.com> writes:

On Friday, 8 February 2019 at 04:51:08 UTC, Sudhi wrote:
 On Friday, 8 February 2019 at 04:30:23 UTC, Arun Chandrasekaran 
 wrote:
 On Friday, 8 February 2019 at 04:13:39 UTC, Sudhi wrote:
 [...]

 Works fine for me with DMD64 D Compiler v2.083.1. 
 https://run.dlang.io/is/RRM8GU


 My example code was wrong. Below is the right one.

 struct Company
 {
     string name;
     string location;
 }

 struct Racks
 {
     int number;
     int location;
 }

 struct Metadata
 {
     string name;
     Company[] companies;
     Racks[] racks;
 }

 struct Item
 {
     Metadata[] met;
     int count;
 }

 shared (Item) item;

 void main()
 {
    updateMetadata();
 }

 void updateMetadata()
 {
    Company company;
    company.name = "Hello";
    company.location = "Bangalore";
    item.met.companies ~= company;
    import std.stdio: writeln;
    writeln(item);
 }

 https://run.dlang.io/is/iem0PY

You have to cast away shared:

auto loc_item = cast(Item) item;
loc_item.met ~= m;
item = cast(shared) loc_item;

Just to be clear, this is not threadsafe and require a mutex if 
you do this other than as init in main.

Feb 07 2019

Eduard Staniloiu <edi33416 gmail.com> writes:

On Friday, 8 February 2019 at 06:55:15 UTC, Jerry wrote:
 On Friday, 8 February 2019 at 04:51:08 UTC, Sudhi wrote:
 On Friday, 8 February 2019 at 04:30:23 UTC, Arun 
 Chandrasekaran wrote:
 On Friday, 8 February 2019 at 04:13:39 UTC, Sudhi wrote:
 [...]

 Works fine for me with DMD64 D Compiler v2.083.1. 
 https://run.dlang.io/is/RRM8GU


 My example code was wrong. Below is the right one.

 struct Company
 {
     string name;
     string location;
 }

 struct Racks
 {
     int number;
     int location;
 }

 struct Metadata
 {
     string name;
     Company[] companies;
     Racks[] racks;
 }

 struct Item
 {
     Metadata[] met;
     int count;
 }

 shared (Item) item;

 void main()
 {
    updateMetadata();
 }

 void updateMetadata()
 {
    Company company;
    company.name = "Hello";
    company.location = "Bangalore";
    item.met.companies ~= company;
    import std.stdio: writeln;
    writeln(item);
 }

 https://run.dlang.io/is/iem0PY

 You have to cast away shared:

 auto loc_item = cast(Item) item;
 loc_item.met ~= m;
 item = cast(shared) loc_item;

 Just to be clear, this is not threadsafe and require a mutex if 
 you do this other than as init in main.

You do not need to cast away shared. You had a couple of issues 
with your `updateMetadata()` function.

First of, `met` is an array, so you need to index it: your code 
`item.met.companies ~= company` becomes `item.met[0].companies ~= 
company`. This will compile, but throw a range error because you 
don't have any `Metadata` object in your `met` array.

I have typed below the revised form of your function

```
void updateMetadata()
{
    // create a Company instance. This must be shared
    shared Company company;
    company.name = "Hello";
    company.location = "Bangalore";

    // create a shared Metadata instance
    shared Metadata m;
    m.name = "m";

    // append m to the array of meta
    item.met ~= m;
    // append the company to the array of companies, for a given 
meta
    item.met[0].companies ~= company;

    import std.stdio: writeln;
    writeln(item);
}
```

The working version is at https://run.dlang.io/is/RvRKrU

Cheers,
Edi

Feb 08 2019

Jonathan M Davis <newsgroup.d jmdavisprog.com> writes:

On Friday, February 8, 2019 4:27:44 AM MST Eduard Staniloiu via Digitalmars-
d-learn wrote:
 On Friday, 8 February 2019 at 06:55:15 UTC, Jerry wrote:
 On Friday, 8 February 2019 at 04:51:08 UTC, Sudhi wrote:
 On Friday, 8 February 2019 at 04:30:23 UTC, Arun

 Chandrasekaran wrote:
 On Friday, 8 February 2019 at 04:13:39 UTC, Sudhi wrote:
 [...]

 Works fine for me with DMD64 D Compiler v2.083.1.
 https://run.dlang.io/is/RRM8GU

 My example code was wrong. Below is the right one.

 struct Company
 {

     string name;
     string location;

 }

 struct Racks
 {

     int number;
     int location;

 }

 struct Metadata
 {

     string name;
     Company[] companies;
     Racks[] racks;

 }

 struct Item
 {

     Metadata[] met;
     int count;

 }

 shared (Item) item;

 void main()
 {

    updateMetadata();

 }

 void updateMetadata()
 {

    Company company;
    company.name = "Hello";
    company.location = "Bangalore";
    item.met.companies ~= company;
    import std.stdio: writeln;
    writeln(item);

 }

 https://run.dlang.io/is/iem0PY

 You have to cast away shared:

 auto loc_item = cast(Item) item;
 loc_item.met ~= m;
 item = cast(shared) loc_item;

 Just to be clear, this is not threadsafe and require a mutex if
 you do this other than as init in main.

 You do not need to cast away shared. You had a couple of issues
 with your `updateMetadata()` function.

 First of, `met` is an array, so you need to index it: your code
 `item.met.companies ~= company` becomes `item.met[0].companies ~=
 company`. This will compile, but throw a range error because you
 don't have any `Metadata` object in your `met` array.

 I have typed below the revised form of your function

 ```
 void updateMetadata()
 {
     // create a Company instance. This must be shared
     shared Company company;
     company.name = "Hello";
     company.location = "Bangalore";

     // create a shared Metadata instance
     shared Metadata m;
     m.name = "m";

     // append m to the array of meta
     item.met ~= m;
     // append the company to the array of companies, for a given
 meta
     item.met[0].companies ~= company;

     import std.stdio: writeln;
     writeln(item);
 }
 ```

 The working version is at https://run.dlang.io/is/RvRKrU

 Cheers,
 Edi

Honestly, the fact that that code compiles is a bug. You're not supposed to
be able to modify shared objects in a manner which isn't guaranteed to be
atomic, because it's not thread-safe. The compiler catches it in a number of
places, but there are many where it currently doesn't.

But regardless of whether the compiler allows such mutation, a mutex (or
similar protection mechanism) needs to be used in order to make the code
thread-safe.

- Jonathan M Davis

Feb 08 2019

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digitalmars.D.learn - Is it possible to modify shared struct array in a function.