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digitalmars.D.learn - Do strings with enum allocate at usage point?

reply =?UTF-8?B?IuWyqeWAiSDmvqoi?= <mio.iwakura gmail.com> writes:
I often hear it advised to avoid using enum with arrays because 
they will allocate at the usage point, but does this also apply 
to strings?
strings are arrays, so naively it seems that they would, but that 
seems odd to me.
I would imagine string literals end up in the data segment as 
they are immutable.

As a continuation of this question, I know that string literals 
have an implicit null delimiter, so it should be correct to pass 
a "literal".ptr to a function taking a C-string, and presumably 
this still applies when using enum.
However, if enum implies allocation at the usage point for 
strings, one would be better served with static, meaning one 
would need to be explicit: static foo = "bar\0"?
Mar 17 2015
next sibling parent reply =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 03/17/2015 11:21 AM, "岩倉 澪" wrote:

 I often hear it advised to avoid using enum with arrays because they
 will allocate at the usage point, but does this also apply to strings?
 strings are arrays, so naively it seems that they would, but that seems
 odd to me.
 I would imagine string literals end up in the data segment as they are
 immutable.

 As a continuation of this question, I know that string literals have an
 implicit null delimiter, so it should be correct to pass a "literal".ptr
 to a function taking a C-string, and presumably this still applies when
 using enum.
 However, if enum implies allocation at the usage point for strings, one
 would be better served with static, meaning one would need to be
 explicit: static foo = "bar\0"?


Strings are fine and fortunately it is very easy to test:

enum arr = [ 1, 2 ];
enum s = "hello";

void main()
{
     assert(arr.ptr !is arr.ptr);
     assert(s.ptr    is s.ptr);
}

Ali
Mar 17 2015
next sibling parent =?UTF-8?B?IuWyqeWAiSDmvqoi?= <mio.iwakura gmail.com> writes:
On Tuesday, 17 March 2015 at 18:25:00 UTC, Ali Çehreli wrote:

 Strings are fine and fortunately it is very easy to test:

 enum arr = [ 1, 2 ];
 enum s = "hello";

 void main()
 {
     assert(arr.ptr !is arr.ptr);
     assert(s.ptr    is s.ptr);
 }

 Ali


Ah, that is good to know. Thanks!
Mar 17 2015
prev sibling parent reply Daniel =?UTF-8?B?S296w6Fr?= via Digitalmars-d-learn writes:
On Tue, 17 Mar 2015 11:25:00 -0700
Ali Çehreli via Digitalmars-d-learn <digitalmars-d-learn puremagic.com>
wrote:


 On 03/17/2015 11:21 AM, "岩倉 澪" wrote:

 I often hear it advised to avoid using enum with arrays because they
 will allocate at the usage point, but does this also apply to
 strings? strings are arrays, so naively it seems that they would,
 but that seems odd to me.
 I would imagine string literals end up in the data segment as they
 are immutable.

 As a continuation of this question, I know that string literals
 have an implicit null delimiter, so it should be correct to pass a
 "literal".ptr to a function taking a C-string, and presumably this
 still applies when using enum.
 However, if enum implies allocation at the usage point for strings,
 one would be better served with static, meaning one would need to be
 explicit: static foo = "bar\0"?


 
 Strings are fine and fortunately it is very easy to test:
 
 enum arr = [ 1, 2 ];
 enum s = "hello";
 
 void main()
 {
      assert(arr.ptr !is arr.ptr);
      assert(s.ptr    is s.ptr);
 }
 
 Ali
 


But is it document somewhere by spec? Or it is just an optimalization
which could be remove at some point?
Mar 18 2015
parent "Marc =?UTF-8?B?U2Now7x0eiI=?= <schuetzm gmx.net> writes:
On Wednesday, 18 March 2015 at 07:58:58 UTC, Daniel Kozák wrote:

 But is it document somewhere by spec? Or it is just an 
 optimalization
 which could be remove at some point?


I cannot find it in the specification, but it is guaranteed. It's 
a benefit we get from the immutability of strings. AFAIK the 
compiler will even merge identical string literals, even when 
they appear in different modules.
Mar 18 2015
prev sibling parent "bearophile" <bearophileHUGS lycos.com> writes:
岩倉 澪:


 However, if enum implies allocation at the usage point for 
 strings,


There are two ways to see if something allocates: there is a 
compiler switch, and an annotation:

void foo()  nogc {
     // Your code here
}

If the compiler doesn't have a bug it will complain if you put 
something that allocates inside that function.

Bye,
bearophile
Mar 18 2015