bug with is(T == TI!TP) expression: captures templated structs but not templated functions?
Dicebot
public at dicebot.lv
Tue Jun 25 03:47:07 PDT 2013
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.
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