• Timothee Cour via Digitalmars-d-learn (13/13) Dec 13 2016 what's the best (and DRY) way to achieve:
• Timon Gehr (5/18) Dec 13 2016 I usually do
• Basile B. (15/40) Dec 14 2016 Strangely if i put this in a templated enum that doesn't work.
• =?UTF-8?Q?Ali_=c3=87ehreli?= (6/16) Dec 14 2016 When you do that, the code does not match the syntax of
• Basile B. (5/26) Dec 14 2016 I see, it makes sense. Anyway the two templates have a common
• Timon Gehr (5/34) Dec 15 2016 Shortcut that works:

Timothee Cour via Digitalmars-d-learn <digitalmars-d-learn puremagic.com> writes:

what's the best (and DRY) way to achieve:

```
static if(__traits(compiles, expr))
  fun(expr);
```

ie, without repeating the expression inside expr?

eg:

```
static if(__traits(compiles, foo.bar[2])){
  counter++;
  writeln(" expr = ", foo.bar[2]);
}

```

Timon Gehr <timon.gehr gmx.ch> writes:

On 14.12.2016 00:00, Timothee Cour via Digitalmars-d-learn wrote:
 what's the best (and DRY) way to achieve:

 ```
 static if(__traits(compiles, expr))
   fun(expr);
 ```

 ie, without repeating the expression inside expr?

 eg:

 ```
 static if(__traits(compiles, foo.bar[2])){
   counter++;
   writeln(" expr = ", foo.bar[2]);
 }

 ```

I usually do

enum code = q{expr};
static if(__traits(compiles,mixin(code)))
     fun(mixin(code));

Basile B. <b2.temp gmx.com> writes:

On Tuesday, 13 December 2016 at 23:37:59 UTC, Timon Gehr wrote:
 On 14.12.2016 00:00, Timothee Cour via Digitalmars-d-learn 
 wrote:
 what's the best (and DRY) way to achieve:

 ```
 static if(__traits(compiles, expr))
   fun(expr);
 ```

 ie, without repeating the expression inside expr?

 eg:

 ```
 static if(__traits(compiles, foo.bar[2])){
   counter++;
   writeln(" expr = ", foo.bar[2]);
 }

 ```

 I usually do

 enum code = q{expr};
 static if(__traits(compiles,mixin(code)))
     fun(mixin(code));

Strangely if i put this in a templated enum that doesn't work.
If instead i use a delegate literal it works.

enum Compiles(string code) = is(typeof((){mixin(code);}));

enum Compiles2(string code) = __traits(compiles, mixin(code));

unittest
{
     static assert(Compiles!q{auto a = 1+1;});
     static assert(!Compiles!q{1;});
     static assert(!Compiles!q{a = 1;});

     static assert(Compiles2!q{auto a = 1+1;});
     static assert(!Compiles2!q{1;});
     static assert(!Compiles2!q{a = 1;});
}

wtf ?

=?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:

On 12/14/2016 09:25 AM, Basile B. wrote:
 On Tuesday, 13 December 2016 at 23:37:59 UTC, Timon Gehr wrote:

 I usually do

 enum code = q{expr};
 static if(__traits(compiles,mixin(code)))
     fun(mixin(code));

 Strangely if i put this in a templated enum that doesn't work.
 If instead i use a delegate literal it works.

 enum Compiles(string code) = is(typeof((){mixin(code);}));

 enum Compiles2(string code) = __traits(compiles, mixin(code));

When you do that, the code does not match the syntax of 
__traits(compiles). Putting the code inside a scope works at least in 
this case:

enum Compiles2(string code) = __traits(compiles, mixin('{' ~ code ~ '}'));

Ali

Basile B. <b2.temp gmx.com> writes:

On Wednesday, 14 December 2016 at 22:06:35 UTC, Ali Çehreli wrote:
 On 12/14/2016 09:25 AM, Basile B. wrote:
 On Tuesday, 13 December 2016 at 23:37:59 UTC, Timon Gehr

 wrote:

 I usually do

 enum code = q{expr};
 static if(__traits(compiles,mixin(code)))
     fun(mixin(code));

 Strangely if i put this in a templated enum that doesn't work.
 If instead i use a delegate literal it works.

 enum Compiles(string code) = is(typeof((){mixin(code);}));

 enum Compiles2(string code) = __traits(compiles, mixin(code));

 When you do that, the code does not match the syntax of 
 __traits(compiles). Putting the code inside a scope works at 
 least in this case:

 enum Compiles2(string code) = __traits(compiles, mixin('{' ~ 
 code ~ '}'));

 Ali

I see, it makes sense. Anyway the two templates have a common 
problem (protection attributes: data used in the code must be 
visible to the outside), so using them as a shortcut is a false 
good idea.

Timon Gehr <timon.gehr gmx.ch> writes:

On 15.12.2016 01:38, Basile B. wrote:
 On Wednesday, 14 December 2016 at 22:06:35 UTC, Ali Çehreli wrote:
 On 12/14/2016 09:25 AM, Basile B. wrote:
 On Tuesday, 13 December 2016 at 23:37:59 UTC, Timon Gehr

 wrote:

 I usually do

 enum code = q{expr};
 static if(__traits(compiles,mixin(code)))
     fun(mixin(code));

 Strangely if i put this in a templated enum that doesn't work.
 If instead i use a delegate literal it works.

 enum Compiles(string code) = is(typeof((){mixin(code);}));

 enum Compiles2(string code) = __traits(compiles, mixin(code));

 When you do that, the code does not match the syntax of
 __traits(compiles). Putting the code inside a scope works at least in
 this case:

 enum Compiles2(string code) = __traits(compiles, mixin('{' ~ code ~
 '}'));

 Ali

 I see, it makes sense. Anyway the two templates have a common problem
 (protection attributes: data used in the code must be visible to the
 outside), so using them as a shortcut is a false good idea.

Shortcut that works:

enum ifCompiles(string code)=`static if(__traits(compiles,{ `~code~` 
})){ `~code~` }`;

mixin(ifCompiles!q{ ... });