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digitalmars.D - constructing module level immutable variables at runtime?

reply Danni Coy via Digitalmars-d <digitalmars-d puremagic.com> writes:
I am trying to port a heavily multithreaded C++ application to D.

I have a lot of variables that are set once from a config file at
runtime and then never change.
It seems that something like the following would be a very clean design.

module config;

static this()
{
    num_triggers = to!int(getValueFromConfigFile());
}

private:
immutable(int) num_triggers = void;

Is there any reason that allowing this would be a bad idea?
Feb 21 2016
next sibling parent reply =?UTF-8?Q?S=c3=b6nke_Ludwig?= <sludwig outerproduct.org> writes:
Am 22.02.2016 um 07:55 schrieb Danni Coy via Digitalmars-d:

 I am trying to port a heavily multithreaded C++ application to D.

 I have a lot of variables that are set once from a config file at
 runtime and then never change.
 It seems that something like the following would be a very clean design.

 module config;

 static this()
 {
      num_triggers = to!int(getValueFromConfigFile());
 }

 private:
 immutable(int) num_triggers = void;

 Is there any reason that allowing this would be a bad idea?


This actually works already, if you use "shared static this". "static 
this" is invoked for each thread that is started, thus it would 
overwrite the existing value of num_triggers, potentially multiple times.
Feb 21 2016
parent reply Danni Coy via Digitalmars-d <digitalmars-d puremagic.com> writes:
On Mon, Feb 22, 2016 at 5:09 PM, Sönke Ludwig
<digitalmars-d puremagic.com> wrote:

 This actually works already, if you use "shared static this". "static this"
 is invoked for each thread that is started, thus it would overwrite the
 existing value of num_triggers, potentially multiple times.


module config;

shared static this ()
{
    num_triggers = 1024;
}

private:
immutable(int) num_triggers = void;

is not working for me with dmd 2.070
Feb 21 2016
parent reply =?UTF-8?Q?S=c3=b6nke_Ludwig?= <sludwig outerproduct.org> writes:
Am 22.02.2016 um 08:27 schrieb Danni Coy via Digitalmars-d:

 On Mon, Feb 22, 2016 at 5:09 PM, Sönke Ludwig
 <digitalmars-d puremagic.com> wrote:

 This actually works already, if you use "shared static this". "static this"
 is invoked for each thread that is started, thus it would overwrite the
 existing value of num_triggers, potentially multiple times.


 module config;

 shared static this ()
 {
      num_triggers = 1024;
 }

 private:
 immutable(int) num_triggers = void;

 is not working for me with dmd 2.070


I was wrong, there is obviously a language/compiler bug here. It 
compiles if you remove the "= void", but it does so for "shared static 
this" as well as for "static this". It really shouldn't in the latter case.
Feb 21 2016
parent reply Danni Coy via Digitalmars-d <digitalmars-d puremagic.com> writes:
On Mon, Feb 22, 2016 at 5:29 PM, Sönke Ludwig
<digitalmars-d puremagic.com> wrote:

 I was wrong, there is obviously a language/compiler bug here. It compiles if
 you remove the "= void", but it does so for "shared static this" as well as
 for "static this". It really shouldn't in the latter case.


Interesting... It definately seems like should work when explicitly
asking the variable not the instantiated and not in a thread local
initialiser.
Feb 21 2016
parent reply Steven Schveighoffer <schveiguy yahoo.com> writes:
On 2/22/16 2:36 AM, Danni Coy via Digitalmars-d wrote:

 On Mon, Feb 22, 2016 at 5:29 PM, Sönke Ludwig
 <digitalmars-d puremagic.com> wrote:

 I was wrong, there is obviously a language/compiler bug here. It compiles if
 you remove the "= void", but it does so for "shared static this" as well as
 for "static this". It really shouldn't in the latter case.


 Interesting... It definately seems like should work when explicitly
 asking the variable not the instantiated and not in a thread local
 initialiser.


I'm not sure the =void has any effect anyway, it's likely just going to 
write the entire static segment with some initial value.

So I'd say remove the =void, and you should be good.

-Steve
Feb 22 2016
parent reply Danni Coy via Digitalmars-d <digitalmars-d puremagic.com> writes:
That worked however it seems that you can only do the assignments
within the shared static this() and not from functions called by the
initialiser which might change how I do things
Feb 22 2016
parent Steven Schveighoffer <schveiguy yahoo.com> writes:
On 2/22/16 9:58 AM, Danni Coy via Digitalmars-d wrote:

 That worked however it seems that you can only do the assignments
 within the shared static this() and not from functions called by the
 initialiser which might change how I do things


This is true. The compiler wants to be super-sure that you are only 
setting it once.

However, this can be alleviated by changing how you do things. Factor 
out the code that sets it, and have it instead return a value. Then you 
can do this:

shared static this() {
    num_triggers = myCrazyFunction();
}

Of course, myCrazyFunction must not depend on any other static 
variables, as those might not be initialized.

startup initialization can be very tricky.

-Steve
Feb 22 2016
prev sibling parent reply =?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:
On 02/21/2016 10:55 PM, Danni Coy via Digitalmars-d wrote:

 I am trying to port a heavily multithreaded C++ application to D.

 I have a lot of variables that are set once from a config file at
 runtime and then never change.
 It seems that something like the following would be a very clean design.

 module config;

 static this()
 {
      num_triggers = to!int(getValueFromConfigFile());
 }

 private:
 immutable(int) num_triggers = void;

 Is there any reason that allowing this would be a bad idea?


There is import() to read a config file at compile time:

module config;

string getValueFromConfigFile() {
     // Assume 'config_file' has just "42" in it:
     auto file_content = import("config_file");
     return file_content;
}

static this()
{
     import std.conv : to;
     num_triggers = to!int(getValueFromConfigFile());
}

private:
immutable(int) num_triggers;    // NOTE: '= void' did not work here

void main() {
     assert(num_triggers == 42);
}

Ali
Feb 21 2016
parent Danni Coy via Digitalmars-d <digitalmars-d puremagic.com> writes:
On Mon, Feb 22, 2016 at 5:14 PM, Ali Çehreli
<digitalmars-d puremagic.com> wrote:


 There is import() to read a config file at compile time:


In my case the config files are there to allow end users to tune the
application - therefore config files need to be read at runtime.
Feb 21 2016