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digitalmars.D.learn - isImplictlyConvertible for Variadic Templates

reply rpeio <rpe rpe.io> writes:
I was wondering whether there was a method built into phobos for 
expanding the "isImplictlyConvertible" template to work for 
variadic templates.

To explain what I mean by this, normally 
"isImplicitlyConvertible(To, From)" checks whether or not a type 
"From" may implicitly be converted to a type "To".

struct Foo(V)
{
     this(V)(V value) if (isImplictlyConvertible!(V, T))
     {
	// do stuff
     }
}

When "From" is variadic, I would like it for each type in "From" 
to be checked whether it may implicitly be converted to type "To".

struct Foo(V)
{
     this(Vs...)(Vs values) if (eachIsImplictlyConvertible!(T, Vs))
     {
	// do stuff
     }
}

This can be accomplished off the top of my head by taking the 
code from std.traits for "isImplicitlyConvertible" and making the 
following change.

template eachIsImplictlyConvertible(To, From...)
{
     enum bool eachIsImplictlyConvertible = is(typeof({
         void fun(ref From vs)
         {
             void gun(To) {}
             foreach (v; vs) // +
             {
                 gun(v);
             }
         }
     }));
}

Implementing this means I have an ostensibly valid method of 
accomplishing what I desire. Though, I am curious whether there's 
a way to facilitate this that is currently available in phobos, 
without having to implement another traits function.

Thanks,
rpeio
Jun 26
parent reply ag0aep6g <anonymous example.com> writes:
On 06/27/2017 02:59 AM, rpeio wrote:
 struct Foo(V)
 {
      this(Vs...)(Vs values) if (eachIsImplictlyConvertible!(T, Vs))
      {
      // do stuff
      }
 }
 
 This can be accomplished off the top of my head by taking the code from 
 std.traits for "isImplicitlyConvertible" and making the following change.
 
[...]
 
 Implementing this means I have an ostensibly valid method of 
 accomplishing what I desire. Though, I am curious whether there's a way 
 to facilitate this that is currently available in phobos, without having 
 to implement another traits function.
---- import std.meta: allSatisfy, ApplyRight; import std.traits: isImplicitlyConvertible; this(Vs...)(Vs values) if (allSatisfy!(ApplyRight!(isImplicitlyConvertible, T), Vs)) { // do stuff } ---- Though, for implicit conversion of all arguments to some type T you can also use this variant of variadic functions: ---- this(T[] values ...) { // do stuff } ----
Jun 26
parent rpeio <rpe rpe.io> writes:
On Tuesday, 27 June 2017 at 01:20:01 UTC, ag0aep6g wrote:
 ----
     import std.meta: allSatisfy, ApplyRight;
     import std.traits: isImplicitlyConvertible;

     this(Vs...)(Vs values)
         if (allSatisfy!(ApplyRight!(isImplicitlyConvertible, 
 T), Vs))
     {
         // do stuff
     }
 ----
That is exactly what I was looking for. I was unaware of the existence of ApplyRight and ApplyLeft. Thank you for your help.
Jun 27