• Taylor Hillegeist (20/20) Jan 07 2020 I'm trying to trick the following code snippet into compilation.
• MoonlightSentinel (17/21) Jan 07 2020 This issue is unrelated to ctRegex, AA literals are non-constant
• Taylor Hillegeist (7/29) Jan 07 2020 Thank you for bringing this to my attention.
• Steven Schveighoffer (13/27) Jan 07 2020 Correct. A compile-time AA is much different in implementation/layout
• Patrick Schluter (5/25) Jan 07 2020 In that specific case: why don't you use an array indexed on

Taylor Hillegeist <taylorh140 gmail.com> writes:

I'm trying to trick the following code snippet into compilation.

enum TokenType{
	//Terminal
	Plus,
	Minus,
	LPer,
	RPer,
	Number,
}

static auto Regexes =[
   TokenType.Plus:   ctRegex!(`^ *\+`),
   TokenType.Minus:  ctRegex!(`^ *\-`),
   TokenType.LPer:   ctRegex!(`^ *\(`),
   TokenType.RPer:   ctRegex!(`^ *\)`),
   TokenType.Number: ctRegex!(`^ *[0-9]+(.[0-9]+)?`)
];

but I can't get it to work. it says its an Error: non-constant 
expression.

I imagine this has to do with the ctRegex template or something. 
maybe there is a better way? Does anyone know?

MoonlightSentinel <moonlightsentinel disroot.org> writes:

On Tuesday, 7 January 2020 at 15:40:58 UTC, Taylor Hillegeist 
wrote:
 but I can't get it to work. it says its an Error: non-constant 
 expression.

 I imagine this has to do with the ctRegex template or 
 something. maybe there is a better way? Does anyone know?

This issue is unrelated to ctRegex, AA literals are non-constant 
expressions (probably due to their implementation). You can work 
around this by using module constructors or lazy initialisation 
inside of a function:

static Regex!char[TokenType] Regexes;

shared static this()
{
     Regexes = [
         TokenType.Plus:   ctRegex!(`^ *\+`),
         TokenType.Minus:  ctRegex!(`^ *\-`),
         TokenType.LPer:   ctRegex!(`^ *\(`),
         TokenType.RPer:   ctRegex!(`^ *\)`),
         TokenType.Number: ctRegex!(`^ *[0-9]+(.[0-9]+)?`)
     ];
}

Taylor Hillegeist <taylorh140 gmail.com> writes:

On Tuesday, 7 January 2020 at 15:51:21 UTC, MoonlightSentinel 
wrote:
 On Tuesday, 7 January 2020 at 15:40:58 UTC, Taylor Hillegeist 
 wrote:
 but I can't get it to work. it says its an Error: non-constant 
 expression.

 I imagine this has to do with the ctRegex template or 
 something. maybe there is a better way? Does anyone know?

 This issue is unrelated to ctRegex, AA literals are 
 non-constant expressions (probably due to their 
 implementation). You can work around this by using module 
 constructors or lazy initialisation inside of a function:

 static Regex!char[TokenType] Regexes;

 shared static this()
 {
     Regexes = [
         TokenType.Plus:   ctRegex!(`^ *\+`),
         TokenType.Minus:  ctRegex!(`^ *\-`),
         TokenType.LPer:   ctRegex!(`^ *\(`),
         TokenType.RPer:   ctRegex!(`^ *\)`),
         TokenType.Number: ctRegex!(`^ *[0-9]+(.[0-9]+)?`)
     ];
 }

Thank you for bringing this to my attention.

also, the solution you used is very cool. I had no idea you could 
put shared static this()
just anywhere and have it execute just like it was in main! Does 
this work for dlls as well?

Steven Schveighoffer <schveiguy gmail.com> writes:

On 1/7/20 11:00 AM, Taylor Hillegeist wrote:
 On Tuesday, 7 January 2020 at 15:51:21 UTC, MoonlightSentinel wrote:
 On Tuesday, 7 January 2020 at 15:40:58 UTC, Taylor Hillegeist wrote:
 but I can't get it to work. it says its an Error: non-constant 
 expression.

 I imagine this has to do with the ctRegex template or something. 
 maybe there is a better way? Does anyone know?

 This issue is unrelated to ctRegex, AA literals are non-constant 
 expressions (probably due to their implementation).


Correct. A compile-time AA is much different in implementation/layout 
than a runtime AA. So you can't initialize them at compile time.

 also, the solution you used is very cool. I had no idea you could put 
 shared static this()
 just anywhere and have it execute just like it was in main! Does this 
 work for dlls as well?

dlls run static constructors upon loading. Thought I'm not too familiar 
with how it exactly works, I know that there can be some trickiness when 
using dlls on Windows.

See information about static constructors/destructors here: 
https://dlang.org/spec/class.html#static-constructor

No idea why it's in the class section, potentially it was only for 
classes at one point?

Information about using DLLs in windows with D is here: 
https://wiki.dlang.org/Win32_DLLs_in_D

-Steve

Patrick Schluter <Patrick.Schluter bbox.fr> writes:

On Tuesday, 7 January 2020 at 15:40:58 UTC, Taylor Hillegeist 
wrote:
 I'm trying to trick the following code snippet into compilation.

 enum TokenType{
 	//Terminal
 	Plus,
 	Minus,
 	LPer,
 	RPer,
 	Number,
 }

 static auto Regexes =[
   TokenType.Plus:   ctRegex!(`^ *\+`),
   TokenType.Minus:  ctRegex!(`^ *\-`),
   TokenType.LPer:   ctRegex!(`^ *\(`),
   TokenType.RPer:   ctRegex!(`^ *\)`),
   TokenType.Number: ctRegex!(`^ *[0-9]+(.[0-9]+)?`)
 ];

 but I can't get it to work. it says its an Error: non-constant 
 expression.

 I imagine this has to do with the ctRegex template or 
 something. maybe there is a better way? Does anyone know?

In that specific case: why don't you use an array indexed on 
TokenType? TokenType are consecutive integrals so indexing is the 
fastest possible access method.