Re: static foreach / How to construct concatenated string?

[MoonlightSentinel via Digitalmars-d-learn]

On Sunday, 8 March 2020 at 20:28:01 UTC, Robert M. Münch wrote:

You can get rid of the enum [...]


That depends on your use case. You will need enum if you want to 
use the value at compile time (e.g. when using it as a template 
parameter). Otherwise a normal string will suffice.



und the static and it will work too.


Yesh, I forgot about the old implicit static foreach loop.

Re: static foreach / How to construct concatenated string?

[Timon Gehr via Digitalmars-d-learn]

On 07.03.20 17:41, MoonlightSentinel wrote:

On Saturday, 7 March 2020 at 16:30:59 UTC, Robert M. Münch wrote:

Is this possible at all?


You can use an anonymous lambda to build the string in CTFE:


It turns out that if you do use this standard idiom, you might end up 
getting blamed for an unrelated DMD bug though:

https://github.com/dlang/dmd/pull/9922

:o)

Re: static foreach / How to construct concatenated string?

[Robert M. Münch via Digitalmars-d-learn]

On 2020-03-07 16:41:47 +, MoonlightSentinel said:


You can use an anonymous lambda to build the string in CTFE:

--

struct S {
 int a;
 bool b;
}

import std;

enum string sql = {
 string s = "CREATE TABLE data(";

 static foreach(f; FieldNameTuple!S) {
s ~= f ~ ",";
 }

s ~= ");";
 return s;
} ();

pragma(msg, sql);

--

This prints "CREATE TABLE data(a, b);"


You can get rid of the enum und the static and it will work too.

--
Robert M. Münch
http://www.saphirion.com
smarter | better | faster

Re: static foreach / How to construct concatenated string?

[Robert M. Münch via Digitalmars-d-learn]

On 2020-03-07 16:41:47 +, MoonlightSentinel said:


On Saturday, 7 March 2020 at 16:30:59 UTC, Robert M. Münch wrote:

Is this possible at all?


You can use an anonymous lambda to build the string in CTFE:

--

struct S {
 int a;
 bool b;
}

import std;

enum string sql = {
 string s = "CREATE TABLE data(";

 static foreach(f; FieldNameTuple!S) {
s ~= f ~ ",";
 }

s ~= ");";
 return s;
} ();

pragma(msg, sql);

--

This prints "CREATE TABLE data(a, b);"


Nice... is the enum a so called "manifest constant" for which the 
initializer is evaluated at compile time?


OT: The pragma seems to print the string twice... at least here on my side.

OT2: Looks like I have to read through the language spec again... and 
most likely over and over again, to have all these tricks at my 
finger-tips.


--
Robert M. Münch
http://www.saphirion.com
smarter | better | faster

Re: static foreach / How to construct concatenated string?

[Robert M. Münch via Digitalmars-d-learn]

On 2020-03-07 16:40:15 +, Adam D. Ruppe said:


Use regular foreach with a regular string. Put that inside a function.

Then simply use that function to initialize your other thing and enjoy 
the magic of CTFE!


Perfect! This implicit CTFE is a tricky thing to see/remember/... 
Feeling a bit dumb but, hey it works :-)


--
Robert M. Münch
http://www.saphirion.com
smarter | better | faster

Re: static foreach / How to construct concatenated string?

[Adam D. Ruppe via Digitalmars-d-learn]

On Saturday, 7 March 2020 at 16:30:59 UTC, Robert M. Münch wrote:
Which of course doesn't work... I didn't find any reference how 
to build-up strings in a statif foreach loop.


Is this possible at all?


Use regular foreach with a regular string. Put that inside a 
function.


Then simply use that function to initialize your other thing and 
enjoy the magic of CTFE!

Re: static foreach / How to construct concatenated string?

[MoonlightSentinel via Digitalmars-d-learn]

On Saturday, 7 March 2020 at 16:30:59 UTC, Robert M. Münch wrote:

Is this possible at all?


You can use an anonymous lambda to build the string in CTFE:

--

struct S {
int a;
bool b;
}

import std;

enum string sql = {
string s = "CREATE TABLE data(";

static foreach(f; FieldNameTuple!S) {
s ~= f ~ ",";
}

s ~= ");";
return s;
} ();

pragma(msg, sql);

--

This prints "CREATE TABLE data(a, b);"

static foreach / How to construct concatenated string?

[Robert M. Münch via Digitalmars-d-learn]

I want to create a "CREATE TABLE data (...)" where the columns are 
derived from struct member names. Something like:


string s = "CREATE TABLE data(";

static foreach(f; FieldNameTuple!myStruct) {
 s ~= f ~ ",";
}

s ~= ");";

Which of course doesn't work... I didn't find any reference how to 
build-up strings in a statif foreach loop.


Is this possible at all?

--
Robert M. Münch
http://www.saphirion.com
smarter | better | faster