• Jonathan Levi (23/23) Apr 02 2020 I am trying to make a templated function for any arguments which
• WebFreak001 (25/48) Apr 03 2020 maybe not the optimal solution because stringof isn't properly
• Jonathan Levi (7/31) Apr 04 2020 I will try that out, thanks. I do have overloads, and somehow I

Jonathan Levi <catanscout gmail.com> writes:

I am trying to make a templated function for any arguments which 
will work for another.

Like this:
```
class Cls {
     auto opBinary(string op, T)(T b)
     if (__traits(compiles, opBinaryImpl!op(this, b)))
     {
         return opBinaryImpl!op(this, b);
     }
}

auto opBinaryImpl(string op, T)(Cls a, T b)
if (isNumeric!T)
{
     // . . .
}
```

Here I use `__traits(compiles)` but if `opBinaryImpl` has a 
compile error in the body than opBinary will claim it does not 
work.

I am looking for something like `__traits(signatureMatch,...)`.

Using std.traits.Parameters does not work because it does not 
work on templates nor does it work with overloading.

WebFreak001 <d.forum webfreak.org> writes:

On Friday, 3 April 2020 at 01:03:01 UTC, Jonathan Levi wrote:
 I am trying to make a templated function for any arguments 
 which will work for another.

 Like this:
 ```
 class Cls {
     auto opBinary(string op, T)(T b)
     if (__traits(compiles, opBinaryImpl!op(this, b)))
     {
         return opBinaryImpl!op(this, b);
     }
 }

 auto opBinaryImpl(string op, T)(Cls a, T b)
 if (isNumeric!T)
 {
     // . . .
 }
 ```

 Here I use `__traits(compiles)` but if `opBinaryImpl` has a 
 compile error in the body than opBinary will claim it does not 
 work.

 I am looking for something like `__traits(signatureMatch,...)`.

 Using std.traits.Parameters does not work because it does not 
 work on templates nor does it work with overloading.

maybe not the optimal solution because stringof isn't properly 
defined, but currently I don't think there is a better way than:

template matchesTemplateConstraints(alias fn, Args...)
{
     enum def = fn.stringof;
     // private void testFun(string op, T)(Cls a, T b) if 
(isNumeric!T) {}
     mixin("private void testFun" ~ def[def.indexOf('(') .. $] ~ " 
{}");

     enum matchesTemplateConstraints = __traits(compiles, 
testFun!Args);
}

void main()
{
     // true
     pragma(msg, matchesTemplateConstraints!(opBinaryImpl, "+", 
int));

     // false
     pragma(msg, matchesTemplateConstraints!(opBinaryImpl, "+", 
string));
}

You can also static foreach over __traits(getOverloads, 
mixin(__MODULE__), "opBinaryImpl", true) if you have multiple 
templates of same name

Jonathan Levi <catanscout gmail.com> writes:

On Friday, 3 April 2020 at 07:08:03 UTC, WebFreak001 wrote:
 maybe not the optimal solution because stringof isn't properly 
 defined, but currently I don't think there is a better way than:

 template matchesTemplateConstraints(alias fn, Args...)
 {
     enum def = fn.stringof;
     // private void testFun(string op, T)(Cls a, T b) if 
 (isNumeric!T) {}
     mixin("private void testFun" ~ def[def.indexOf('(') .. $] ~ 
 " {}");

     enum matchesTemplateConstraints = __traits(compiles, 
 testFun!Args);
 }

 void main()
 {
     // true
     pragma(msg, matchesTemplateConstraints!(opBinaryImpl, "+", 
 int));

     // false
     pragma(msg, matchesTemplateConstraints!(opBinaryImpl, "+", 
 string));
 }

 You can also static foreach over __traits(getOverloads, 
 mixin(__MODULE__), "opBinaryImpl", true) if you have multiple 
 templates of same name

I will try that out, thanks.  I do have overloads, and somehow I 
missed the existence of `__traits(getOverloads)`.


Ah, I see, take the string of the function code (didn't know you 
could do that...) and create a local duplicate without the body 
included.  Hacky, but a workable solution if D does not have 
anything better.