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digitalmars.D.learn - Allocate a string via the GC

reply JG <someone somewhere.com> writes:
Hi,

Is there any more standard way to achieve something to the effect 
of:

```d
   import std.experimental.allocator;
   string* name = theAllocator.make!string;
  ```
May 23 2022
next sibling parent reply Adam D Ruppe <destructionator gmail.com> writes:
On Monday, 23 May 2022 at 09:38:07 UTC, JG wrote:

 Hi,

 Is there any more standard way to achieve something to the 
 effect of:

 ```d
   import std.experimental.allocator;
   string* name = theAllocator.make!string;
  ```


Why do you want that?

Easiest way I know of is to just wrap it in a struct, then `new 
that_struct`, which is also a better way for all the use cases I 
know.... but those use cases are pretty rare so there's probably 
a better way to do what you're trying to do.
May 23 2022
next sibling parent reply bauss <jj_1337 live.dk> writes:
On Monday, 23 May 2022 at 11:39:22 UTC, Adam D Ruppe wrote:

 On Monday, 23 May 2022 at 09:38:07 UTC, JG wrote:

 Hi,

 Is there any more standard way to achieve something to the 
 effect of:

 ```d
   import std.experimental.allocator;
   string* name = theAllocator.make!string;
  ```


 Why do you want that?

 Easiest way I know of is to just wrap it in a struct, then `new 
 that_struct`, which is also a better way for all the use cases 
 I know.... but those use cases are pretty rare so there's 
 probably a better way to do what you're trying to do.


My guess is  nogc in which case your solution doesn't work.

Same with Ferhat's examples.
May 23 2022
parent bauss <jj_1337 live.dk> writes:
On Monday, 23 May 2022 at 12:17:56 UTC, bauss wrote:

 On Monday, 23 May 2022 at 11:39:22 UTC, Adam D Ruppe wrote:

 On Monday, 23 May 2022 at 09:38:07 UTC, JG wrote:

 Hi,

 Is there any more standard way to achieve something to the 
 effect of:

 ```d
   import std.experimental.allocator;
   string* name = theAllocator.make!string;
  ```


 Why do you want that?

 Easiest way I know of is to just wrap it in a struct, then 
 `new that_struct`, which is also a better way for all the use 
 cases I know.... but those use cases are pretty rare so 
 there's probably a better way to do what you're trying to do.


 My guess is  nogc in which case your solution doesn't work.

 Same with Ferhat's examples.


Oops wait, I just saw that it says "via the GC" in the title. I 
completely missed that until I had of course sent my other 
message.
May 23 2022
prev sibling parent reply JG <someone somewhere.com> writes:
On Monday, 23 May 2022 at 11:39:22 UTC, Adam D Ruppe wrote:

 On Monday, 23 May 2022 at 09:38:07 UTC, JG wrote:

 Hi,

 Is there any more standard way to achieve something to the 
 effect of:

 ```d
   import std.experimental.allocator;
   string* name = theAllocator.make!string;
  ```


 Why do you want that?

 Easiest way I know of is to just wrap it in a struct, then `new 
 that_struct`, which is also a better way for all the use cases 
 I know.... but those use cases are pretty rare so there's 
 probably a better way to do what you're trying to do.


I am writing an interpreter and I needed access to a string via
a pointer of type void*

I ended up wrapping it in a struct since I needed another value
anyway. Seems odd that one can't do it in a less unusual way.

Thanks.
May 23 2022
next sibling parent bauss <jj_1337 live.dk> writes:
On Monday, 23 May 2022 at 12:20:11 UTC, JG wrote:

 On Monday, 23 May 2022 at 11:39:22 UTC, Adam D Ruppe wrote:

 On Monday, 23 May 2022 at 09:38:07 UTC, JG wrote:

 Hi,

 Is there any more standard way to achieve something to the 
 effect of:

 ```d
   import std.experimental.allocator;
   string* name = theAllocator.make!string;
  ```


 Why do you want that?

 Easiest way I know of is to just wrap it in a struct, then 
 `new that_struct`, which is also a better way for all the use 
 cases I know.... but those use cases are pretty rare so 
 there's probably a better way to do what you're trying to do.


 I am writing an interpreter and I needed access to a string via
 a pointer of type void*

 I ended up wrapping it in a struct since I needed another value
 anyway. Seems odd that one can't do it in a less unusual way.

 Thanks.


You can take the address of the string. .ptr should do it, BUT I 
think it might not always work, someone can correct me on this, 
but I believe it depends on where the memory for the string lives 
whether it works or not?
May 23 2022
prev sibling parent Adam D Ruppe <destructionator gmail.com> writes:
On Monday, 23 May 2022 at 12:20:11 UTC, JG wrote:

 I am writing an interpreter and I needed access to a string via
 a pointer of type void*

 I ended up wrapping it in a struct since I needed another value
 anyway. Seems odd that one can't do it in a less unusual way.


OK yeah, that's the main use case I'd think of, and that's also 
exactly why I think doing the struct is the best thing anyway 
since you can bundle whatever you need in there instead of just a 
single value.
May 23 2022
prev sibling parent Ferhat =?UTF-8?B?S3VydHVsbXXFnw==?= <aferust gmail.com> writes:
On Monday, 23 May 2022 at 09:38:07 UTC, JG wrote:

 Hi,

 Is there any more standard way to achieve something to the 
 effect of:

 ```d
   import std.experimental.allocator;
   string* name = theAllocator.make!string;
  ```


Pointers are not used for strings in d. string is an alias for 
immutable(char)[]. So, you can do:
```d
     import std.exception : assumeUnique; // makes char[] immutable

     string str = (new char[15]).assumeUnique;

     str = "hmm. my string!";
```

a slice in d (e.g. char[]) is roughly considered as a struct with 
a pointer and length. I also suspect that your question is not 
that simple, maybe you really need a string pointer, and I 
couldn't understand what you are actually asking. I am sorry if 
those are not what you were looking for the answers to.

Here is how you GC allocate a pointer to a string.
```d
string* strptr = new string[1].ptr;
// Since slices are reference types just use this instead:
string[] strptr = new string[1];
```
Maybe you need a pointer to the first char of a string then:
```d
string str; // allocated somehow

immutable(char)* chr = str.ptr;
```
May 23 2022