• Jack Applegame (24/24) Mar 21 2021 Could someone please explain what is wrong with this code?
• Imperatorn (2/26) Mar 21 2021 https://forum.dlang.org/thread/mggbomxhjpglltsihqek@forum.dlang.org
• Jack Applegame (2/33) Mar 21 2021 There are no non-global templates in my snippet.
• Steven Schveighoffer (18/47) Mar 21 2021 You have the wrong lines attributed with the error message. The error
• MichaelJames (2/26) Mar 22 2021 Tell me, did you manage to solve this problem?
• Nicholas Wilson (2/3) Mar 23 2021 https://github.com/dlang/dmd/pull/12300

Jack Applegame <japplegame gmail.com> writes:

Could someone please explain what is wrong with this code?

https://glot.io/snippets/fwxn2198kv

```d
import std.stdio;

struct Sample{
   void function() func1;
   void function() func2;
}

void noth(Sample smpl)() {
   smpl.func1(); // Error: expression __lambda1 is not a valid 
template value argument
   smpl.func2(); // Error: expression __lambda2 is not a valid 
template value argument
}

void main(){
   enum s = Sample(
     {writeln("Hello world1");},
     {writeln("Hello world2");}
   );
   s.func1();
   s.func2();
   noth!(s)();
}
```

Imperatorn <johan_forsberg_86 hotmail.com> writes:

On Sunday, 21 March 2021 at 07:18:10 UTC, Jack Applegame wrote:
 Could someone please explain what is wrong with this code?

 https://glot.io/snippets/fwxn2198kv

 ```d
 import std.stdio;

 struct Sample{
   void function() func1;
   void function() func2;
 }

 void noth(Sample smpl)() {
   smpl.func1(); // Error: expression __lambda1 is not a valid 
 template value argument
   smpl.func2(); // Error: expression __lambda2 is not a valid 
 template value argument
 }

 void main(){
   enum s = Sample(
     {writeln("Hello world1");},
     {writeln("Hello world2");}
   );
   s.func1();
   s.func2();
   noth!(s)();
 }
 ```

https://forum.dlang.org/thread/mggbomxhjpglltsihqek forum.dlang.org

Jack Applegame <japplegame gmail.com> writes:

On Sunday, 21 March 2021 at 08:45:19 UTC, Imperatorn wrote:
 On Sunday, 21 March 2021 at 07:18:10 UTC, Jack Applegame wrote:
 Could someone please explain what is wrong with this code?

 https://glot.io/snippets/fwxn2198kv

 ```d
 import std.stdio;

 struct Sample{
   void function() func1;
   void function() func2;
 }

 void noth(Sample smpl)() {
   smpl.func1(); // Error: expression __lambda1 is not a valid 
 template value argument
   smpl.func2(); // Error: expression __lambda2 is not a valid 
 template value argument
 }

 void main(){
   enum s = Sample(
     {writeln("Hello world1");},
     {writeln("Hello world2");}
   );
   s.func1();
   s.func2();
   noth!(s)();
 }
 ```

 https://forum.dlang.org/thread/mggbomxhjpglltsihqek forum.dlang.org

There are no non-global templates in my snippet.

Steven Schveighoffer <schveiguy gmail.com> writes:

On 3/21/21 3:18 AM, Jack Applegame wrote:
 Could someone please explain what is wrong with this code?
 
 https://glot.io/snippets/fwxn2198kv
 
 ```d
 import std.stdio;
 
 struct Sample{
    void function() func1;
    void function() func2;
 }
 
 void noth(Sample smpl)() {
    smpl.func1(); // Error: expression __lambda1 is not a valid template 
 value argument
    smpl.func2(); // Error: expression __lambda2 is not a valid template 
 value argument
 }
 
 void main(){
    enum s = Sample(
      {writeln("Hello world1");},
      {writeln("Hello world2");}
    );
    s.func1();
    s.func2();
    noth!(s)();
 }
 ```

You have the wrong lines attributed with the error message. The error 
message is in the assignment of s (line 15 and 16)

Essentially, you can't use lambda functions as compile-time values.

Valid template value parameters are [1]

"any type which can be statically initialized at compile time. Template 
value arguments can be integer values, floating point values, nulls, 
string values, array literals of template value arguments, associative 
array literals of template value arguments, or struct literals of 
template value arguments."

Now, one might argue that it's possible to statically initialize 
function pointers at compile time (i.e. you can do this as a static 
initialized function pointer at module scope), so possibly this is 
something that can be fixed. There might already be a bug report on it, 
or you can file one. It might end up with the spec being clarified to 
explicitly cover this case.

-Steve

[1] https://dlang.org/spec/template.html#template_value_parameter

MichaelJames <MichaelJamesuN63 yahoo.com> writes:

On Sunday, 21 March 2021 at 07:18:10 UTC, Jack Applegame wrote:
 Could someone please explain what is wrong with this code?

 https://glot.io/snippets/fwxn2198kv

 ```d
 import std.stdio;

 struct Sample{
   void function() func1;
   void function() func2;
 }

 void noth(Sample smpl)() {
   smpl.func1(); // Error: expression __lambda1 is not a valid 
 template value argument
   smpl.func2(); // Error: expression __lambda2 is not a valid 
 template value argument
 }

 void main(){
   enum s = Sample(
     {writeln("Hello world1");},
     {writeln("Hello world2");}
   );
   s.func1();
   s.func2();
   noth!(s)();
 }
 ```

Tell me, did you manage to solve this problem?

Nicholas Wilson <iamthewilsonator hotmail.com> writes:

On Monday, 22 March 2021 at 07:52:14 UTC, MichaelJames wrote:
 Tell me, did you manage to solve this problem?

https://github.com/dlang/dmd/pull/12300