• learnfirst1 (28/28) Aug 10 2018 import core.stdc.stdio;
• rikki cattermole (5/42) Aug 10 2018 Without the brackets it is inferring to not have state and hence is a
• Paul Backus (8/24) Aug 10 2018 The arrow syntax doesn't work for multi-line lambdas; you need to
• Simen =?UTF-8?B?S2rDpnLDpXM=?= (14/17) Aug 10 2018 This is not doing what you think it's doing. The syntax t => {
• learnfirst1 (6/13) Aug 10 2018 rikki cattermole , Paul Backus, Simen Kjærås: thanks for the
• Paul Backus (3/6) Aug 10 2018 If you make your main function @nogc, you will get a compile-time

learnfirst1 <learnfirst1 gmail.com> writes:

import core.stdc.stdio;

struct Test {
	string name ;
}

void T(alias pred, A...)(){
	__gshared t = Test(A) ;
	 pred(t);
}

extern(C) void main(){
	T!(t => printf("test 1 name = %s\n".ptr, t.name.ptr), "test") ;  
// build OK
	T!(t => {
		printf("test 2 name = %s\n".ptr, t.name.ptr);
	}, "test") ; // build error
}

--------------

build this with betterC

Undefined symbols for architecture x86_64:
   "__d_allocmemory", referenced from:
       __D4test4mainUZ__T9__lambda2TSQBb4TestZQvFNaNbNfQtZDFNbNiZv 
in test.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to 
see invocation)
Error: linker exited with status 1


to use without {}, it work as expect.

Is there a way to avoid this GC with {}, because we need multi 
line here.

rikki cattermole <rikki cattermole.co.nz> writes:

On 10/08/2018 9:57 PM, learnfirst1 wrote:
 
 import core.stdc.stdio;
 
 struct Test {
      string name ;
 }
 
 void T(alias pred, A...)(){
      __gshared t = Test(A) ;
       pred(t);
 }
 
 extern(C) void main(){
      T!(t => printf("test 1 name = %s\n".ptr, t.name.ptr), "test") ; // 
 build OK
      T!(t => {
          printf("test 2 name = %s\n".ptr, t.name.ptr);
      }, "test") ; // build error
 }
 
 --------------
 
 build this with betterC
 
 Undefined symbols for architecture x86_64:
    "__d_allocmemory", referenced from:
        __D4test4mainUZ__T9__lambda2TSQBb4TestZQvFNaNbNfQtZDFNbNiZv in 
 test.o
 ld: symbol(s) not found for architecture x86_64
 clang: error: linker command failed with exit code 1 (use -v to see 
 invocation)
 Error: linker exited with status 1
 
 
 to use without {}, it work as expect.
 
 Is there a way to avoid this GC with {}, because we need multi line here.

Without the brackets it is inferring to not have state and hence is a 
function. But with the brackets it is assuming there is state required 
and hence has to allocate. Without manually allocating said state (not 
what you want), you cannot do this.

Paul Backus <snarwin gmail.com> writes:

On Friday, 10 August 2018 at 09:57:53 UTC, learnfirst1 wrote:
 import core.stdc.stdio;

 struct Test {
 	string name ;
 }

 void T(alias pred, A...)(){
 	__gshared t = Test(A) ;
 	 pred(t);
 }

 extern(C) void main(){
 	T!(t => printf("test 1 name = %s\n".ptr, t.name.ptr), "test") 
 ;  // build OK
 	T!(t => {
 		printf("test 2 name = %s\n".ptr, t.name.ptr);
 	}, "test") ; // build error
 }

 --------------

The arrow syntax doesn't work for multi-line lambdas; you need to 
write them using what the spec calls "function literal" syntax 
[1]:

     T!((t) { // <- Parens around the argument, no arrow
         printf("test 2 name = %s\n".ptr, t.name.ptr);
     }, "test") ;

[1] https://dlang.org/spec/expression.html#function_literals

Simen =?UTF-8?B?S2rDpnLDpXM=?= <simen.kjaras gmail.com> writes:

On Friday, 10 August 2018 at 09:57:53 UTC, learnfirst1 wrote:
 	T!(t => {
 		printf("test 2 name = %s\n".ptr, t.name.ptr);
 	}, "test") ; // build error

This is not doing what you think it's doing. The syntax t => { 
return t; } is equivalent to t => () => t. That is, it's 
returning a function that takes no arguments, not a value.

For that very same reason, if you compile and run your code 
without -betterC, only the first printf() will be executed, and 
only one line of output will be generated.

What you should do instead is:
     T!((t){
             printf("test 2 name = %s\n".ptr, t.name.ptr);
         }, "test");

(note the lack of the => arrow)

--
   Simen

learnfirst1 <learnfirst1 gmail.com> writes:

On Friday, 10 August 2018 at 10:38:53 UTC, Simen Kjærås wrote:
 What you should do instead is:
     T!((t){
             printf("test 2 name = %s\n".ptr, t.name.ptr);
         }, "test");

 (note the lack of the => arrow)

 --
   Simen


rikki cattermole , Paul Backus, Simen Kjærås: thanks for the 
explain, it work.


Still,  if my first example is use GC, why dmd not throw error at 
compile time, instead at link time report symbols is missing.   
Is this a bug ?

Paul Backus <snarwin gmail.com> writes:

On Friday, 10 August 2018 at 11:10:55 UTC, learnfirst1 wrote:
 Still,  if my first example is use GC, why dmd not throw error 
 at compile time, instead at link time report symbols is 
 missing.   Is this a bug ?

If you make your main function  nogc, you will get a compile-time 
error.