As far as I known, when I define a string with enum and it is used at different parts of code, that string is repeated again and again in executable file instead of passing a pointer to string. So, using enum with string doesn't seem like a good idea.

Hence, I defined string as const to make it belong to struct itself instead of instances, but it comes with 'need `this` for ...' error. This indicates that the string doesn't belong to struct itself actually.

Because there is nothing like namespace in D, I used a sub-struct.

[code]
struct TableSchema{
	const string TABLE = "users";

	struct FieldTypes{
		const string ID = "BIGINT";
	}

	const string CREATESQL = "... id " ~ FieldTypes.ID ~ "...";
}
[/code]


But compiler doesn't allow me to access FieldTypes.ID. It says that it needs `this`. I tried with `static shared`, used `class` instead of `struct` etc. But couldn't have come up with a nice solution.

On Tuesday, 16 June 2015 at 21:17:37 UTC, tcak wrote:
> As far as I known, when I define a string with enum and it is used at different parts of code, that string is repeated again and again in executable file instead of passing a pointer to string. So, using enum with string doesn't seem like a good idea.
>
> Hence, I defined string as const to make it belong to struct itself instead of instances, but it comes with 'need `this` for ...' error. This indicates that the string doesn't belong to struct itself actually.
>
> Because there is nothing like namespace in D, I used a sub-struct.
>
> [code]
> struct TableSchema{
> 	const string TABLE = "users";
>
> 	struct FieldTypes{
> 		const string ID = "BIGINT";
> 	}
>
> 	const string CREATESQL = "... id " ~ FieldTypes.ID ~ "...";
> }
> [/code]
>
>
> But compiler doesn't allow me to access FieldTypes.ID. It says that it needs `this`. I tried with `static shared`, used `class` instead of `struct` etc. But couldn't have come up with a nice solution.

Do i miss a detail in your requirement ?

---
struct TableSchema{
	const string TABLE = "users";

	struct FieldTypes{
		static const string ID = "BIGINT";
	}

	const string CREATESQL = "... id " ~ FieldTypes.ID ~ "...";
}
---

because this works.

On Tuesday, 16 June 2015 at 21:38:22 UTC, jklp wrote:
> On Tuesday, 16 June 2015 at 21:17:37 UTC, tcak wrote:
>> [...]
>
> Do i miss a detail in your requirement ?
>
> ---
> struct TableSchema{
> 	const string TABLE = "users";
>
> 	struct FieldTypes{
> 		static const string ID = "BIGINT";
> 	}
>
> 	const string CREATESQL = "... id " ~ FieldTypes.ID ~ "...";
> }
> ---
>
> because this works.

Hmm, I never defined it as `static const` before. Tried with `static shared` only. Yes, it works like this.

On Tuesday, 16 June 2015 at 21:17:37 UTC, tcak wrote:
> As far as I known, when I define a string with enum and it is used at different parts of code, that string is repeated again and again in executable file instead of passing a pointer to string. So, using enum with string doesn't seem like a good idea.
>

I'm not sure how true that is. For example, this prints the same address twice:
----
import std.stdio;
enum e = "foo";
void main()
{
    auto a = e;
    auto b = e;
    writeln(a.ptr);
    writeln(b.ptr);
}
----

In contrast, it prints two different addresses when e is defined as `[1, 2, 3]` instead.

[...]
>
> [code]
> struct TableSchema{
> 	const string TABLE = "users";
>
> 	struct FieldTypes{
> 		const string ID = "BIGINT";
> 	}
>
> 	const string CREATESQL = "... id " ~ FieldTypes.ID ~ "...";
> }
> [/code]
>
>
> But compiler doesn't allow me to access FieldTypes.ID. It says that it needs `this`. I tried with `static shared`, used `class` instead of `struct` etc. But couldn't have come up with a nice solution.

`static immutable` is where it's at.

On Tuesday, 16 June 2015 at 21:17:37 UTC, tcak wrote:
> As far as I known, when I define a string with enum and it is used at different parts of code, that string is repeated again and again in executable file instead of passing a pointer to string. So, using enum with string doesn't seem like a good idea.

String literals are merged by the compiler, much like in C and Java.

import std.stdio;
enum mystring = "hello world!";

void main() {
	string str1 = mystring;
	string str2 = mystring;
	
	writeln(str1.ptr == str2.ptr); // prints true
}

On 6/17/2015 6:17 AM, tcak wrote:
> As far as I known, when I define a string with enum and it is used at
> different parts of code, that string is repeated again and again in
> executable file instead of passing a pointer to string. So, using enum
> with string doesn't seem like a good idea.
>
The string is not repeated again and again in the *executable*. The compiler is smart enough to recognize the same string is used in multiple places. It will be placed in the data segment only once. It's no different than using a string literal.

On Wed, 17 Jun 2015 09:49:56 +0900, Mike Parker wrote:

> On 6/17/2015 6:17 AM, tcak wrote:
>> As far as I known, when I define a string with enum and it is used at different parts of code, that string is repeated again and again in executable file instead of passing a pointer to string. So, using enum with string doesn't seem like a good idea.
>>
> The string is not repeated again and again in the *executable*. The compiler is smart enough to recognize the same string is used in multiple places. It will be placed in the data segment only once. It's no different than using a string literal.

but only to some extent[1].

[1] https://issues.dlang.org/show_bug.cgi?id=14459