Hi there, I'm having trouble getting the following code to compile:

import std.stdio;

string a = "a";
string b = a;

void main()
{
    writeln(b);
}

DMD spits out the error "test.d(4): Error: variable a cannot be read at compile time". Is there any way to tell the compiler I want b evaluated at runtime, or am I missing something obvious here?

On Wednesday, 15 August 2012 at 13:36:26 UTC, Stefan wrote:
> Hi there, I'm having trouble getting the following code to compile:
>
> import std.stdio;
>
> string a = "a";
> string b = a;
>
> void main()
> {
>     writeln(b);
> }
>
> DMD spits out the error "test.d(4): Error: variable a cannot be read at compile time". Is there any way to tell the compiler I want b evaluated at runtime, or am I missing something obvious here?

Make a an enum, const or otherwise immutable.

On Wednesday, 15 August 2012 at 13:41:10 UTC, RommelVR wrote:
> Make a an enum, const or otherwise immutable.

I don't think you understood the question.

On Wednesday, 15 August 2012 at 13:36:26 UTC, Stefan wrote:
> Hi there, I'm having trouble getting the following code to compile:
>
> import std.stdio;
>
> string a = "a";
> string b = a;        // line 4
>
> void main()
> {
>     writeln(b);       // line 8
> }
>
> DMD spits out the error "test.d(4): Error: variable a cannot be read at compile time". Is there any way to tell the compiler I want b evaluated at runtime, or am I missing something obvious here?

You must understand that your problem lies in line 4, not in line 8, i.e. the following doesn't work either:

string a = "a";
string b = a;

I don't really know why, but it seems that you can only initialize globals with constants.

What you could do is something like this (I guess):

enum value = "a";
string a = value;
string b = value;

void main()
{
    writeln(b);
    b = "b";
    writeln(b);
}

On Wednesday, 15 August 2012 at 13:36:26 UTC, Stefan wrote:
> Hi there, I'm having trouble getting the following code to compile:
>
> import std.stdio;
>
> string a = "a";
> string b = a;
>
> void main()
> {
>     writeln(b);
> }
>
> DMD spits out the error "test.d(4): Error: variable a cannot be read at compile time". Is there any way to tell the compiler I want b evaluated at runtime, or am I missing something obvious here?

untested

string a = "a";

static this() {
    string b = a;
}

be aware of the details:

http://dlang.org/module.html#staticorder

On 8/15/12, d_follower <d_follower@fakemail.com> wrote:
> I don't really know why, but it seems that you can only initialize globals with constants.

That's what the static constructor is for: http://dlang.org/class.html#StaticConstructor http://dlang.org/class.html#SharedStaticConstructor

On Wed, 15 Aug 2012 15:36:24 +0200, Stefan wrote:

> Hi there, I'm having trouble getting the following code to compile:
> 
> import std.stdio;
> 
> string a = "a";
> string b = a;
> 
> void main()
> {
>      writeln(b);
> }
> 
> DMD spits out the error "test.d(4): Error: variable a cannot be read at compile time". Is there any way to tell the compiler I want b evaluated at runtime, or am I missing something obvious here?

D is not as context-sensitive as what you may be used to. This is a feature to make the language more parseable and human-grokable. Basically, the result of a module-level assignment should not depend on what came before, so this example code is invalid:

string a = "a";
a = "b";
string b = a;

This would require the declaration of b to depend on the order of the declarations/statements which come before it.  When you add in the import of modules, things would get really hairy really fast. So module-level declarations must use constant expressions (literals or symbols to constant data) in their initialization.

Justin

On 08/15/2012 06:55 AM, d_follower wrote:
> On Wednesday, 15 August 2012 at 13:41:10 UTC, RommelVR wrote:
>> Make a an enum, const or otherwise immutable.
>
> I don't think you understood the question.

I thought RommelVR did understand the question. Try this:

import std.stdio;

enum a = "a";
string b = a;

void main()
{
    writeln(b);
}

Ali

-- 
D Programming Language Tutorial: http://ddili.org/ders/d.en/index.html

Another option is to use "module constructors", as shown below. (But somehow this all looks a bit fishy for me...)

LMB

----

import std.stdio;

string a = "a";
string b;

static this()
{
   b = a;
}

void main()
{
   writeln(b);
}


On Wed, Aug 15, 2012 at 11:03 AM, d_follower <d_follower@fakemail.com> wrote:
> On Wednesday, 15 August 2012 at 13:36:26 UTC, Stefan wrote:
>>
>> Hi there, I'm having trouble getting the following code to compile:
>>
>> import std.stdio;
>>
>> string a = "a";
>> string b = a;        // line 4
>>
>> void main()
>> {
>>     writeln(b);       // line 8
>>
>> }
>>
>> DMD spits out the error "test.d(4): Error: variable a cannot be read at compile time". Is there any way to tell the compiler I want b evaluated at runtime, or am I missing something obvious here?
>
>
> You must understand that your problem lies in line 4, not in line 8, i.e. the following doesn't work either:
>
>
> string a = "a";
> string b = a;
>
> I don't really know why, but it seems that you can only initialize globals with constants.
>
> What you could do is something like this (I guess):
>
> enum value = "a";
> string a = value;
> string b = value;
>
> void main()
> {
>     writeln(b);
>     b = "b";
>     writeln(b);
> }

I have got same error. I need to pass in instance of class constant, but got error "Error: static variable  cannot be read at compile"

http://www.everfall.com/paste/id.php?1mc9mb9cxyie

When I had create instance of class in main, and create confvarible above it all worked, but when I had moved it's in module I got error.