Allocate a string via the GC

May 23, 2022

Adam D Ruppe

May 23, 2022

bauss

May 23, 2022

May 23, 2022

May 23, 2022

May 23, 2022

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

Re: Allocate a string via the GC

Posted by Ferhat Kurtulmuş
in reply to JG

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Ferhat Kurtulmuş

Posted in reply to JG

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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:

  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:

    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.

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:

string str; // allocated somehow

immutable(char)* chr = str.ptr;

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.

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.

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.

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?

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.

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