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digitalmars.D - bug with is(T == TI!TP) expression: captures templated structs but

reply Timothee Cour <thelastmammoth gmail.com> writes:
template Test(alias T){
  static if(is(T == TI!TP, alias TI, TP)){
    enum Test=true;
  }
  else{
    enum Test=false;
  }
}

struct A(T){}
void foo(T)(T a){}

void main(){
  static assert(Test!(A!double));
  static assert(!Test!(foo!double)); //why is Test false?
}

This is blocking my pull request to make
fullyQualifiedName/GetTemplateParent/GetTemplateArguments work on
everything: right now it fails on templated functions.
Jun 25 2013
next sibling parent Timon Gehr <timon.gehr gmx.ch> writes:
On 06/25/2013 12:32 PM, Timothee Cour wrote:

It is not a bug.

 template Test(alias T){
    static if(is(T == TI!TP, alias TI, TP)){
      enum Test=true;
    }
    else{
      enum Test=false;
    }
 }

 struct A(T){}
 void foo(T)(T a){}

 void main(){
    static assert(Test!(A!double));
    static assert(!Test!(foo!double)); //why is Test false?
 }

Because foo!double is not a type. All forms of the is-expression check whether the first argument is a valid type.
 This is blocking my pull request to make
 fullyQualifiedName/GetTemplateParent/GetTemplateArguments work on
 everything: right now it fails on templated functions.

Jun 25 2013
prev sibling parent reply "Dicebot" <public dicebot.lv> writes:
On Tuesday, 25 June 2013 at 10:32:14 UTC, Timothee Cour wrote:
 template Test(alias T){
   static if(is(T == TI!TP, alias TI, TP)){
     enum Test=true;
   }
   else{
     enum Test=false;
   }
 }

 struct A(T){}
 void foo(T)(T a){}

 void main(){
   static assert(Test!(A!double));
   static assert(!Test!(foo!double)); //why is Test false?
 }

 This is blocking my pull request to make
 fullyQualifiedName/GetTemplateParent/GetTemplateArguments work 
 on
 everything: right now it fails on templated functions.

As I have already mentiond in comments to that pull (probably was not clear enough), it is not really a bug, but one of many difficulties when working with function types in generic code. When you pass a function there, you pass function symbol, not its type. For aggregates those are interchangeable, not so for functions. Most simple example: void foo(int x) {} pragma( msg, is(foo == function) ); // false pragma( msg, is(typeof(foo) == function) ); // true So you simply can't do any type matching with T when T is function alias. However, when you take typeof(T), all template information gets lost and you get type of specific instantiation. Looks like not a bug, but lack of required tool.
Jun 25 2013
parent Timothee Cour <thelastmammoth gmail.com> writes:
On Tue, Jun 25, 2013 at 3:47 AM, Dicebot <public dicebot.lv> wrote:

 On Tuesday, 25 June 2013 at 10:32:14 UTC, Timothee Cour wrote:

 template Test(alias T){
   static if(is(T == TI!TP, alias TI, TP)){
     enum Test=true;
   }
   else{
     enum Test=false;
   }
 }

 struct A(T){}
 void foo(T)(T a){}

 void main(){
   static assert(Test!(A!double));
   static assert(!Test!(foo!double)); //why is Test false?
 }

 This is blocking my pull request to make
 fullyQualifiedName/**GetTemplateParent/**GetTemplateArguments work on
 everything: right now it fails on templated functions.

As I have already mentiond in comments to that pull (probably was not clear enough), it is not really a bug, but one of many difficulties when working with function types in generic code. When you pass a function there, you pass function symbol, not its type. For aggregates those are interchangeable, not so for functions. Most simple example: void foo(int x) {} pragma( msg, is(foo == function) ); // false pragma( msg, is(typeof(foo) == function) ); // true So you simply can't do any type matching with T when T is function alias. However, when you take typeof(T), all template information gets lost and you get type of specific instantiation. Looks like not a bug, but lack of required tool.

So how can I decompose alias fun=foo!double into template parent / template arguments? The compiler knows this so there has to be a way to retrieve it. If not, then we're back in my previous proposal, adding: __traits(templateParent, symbol) __traits(templateArguments, symbol)
Jun 25 2013