On Sunday, 20 January 2013 at 16:11:08 UTC, Philippe Sigaud wrote:
On Sun, Jan 20, 2013 at 5:01 PM, Phil Lavoie
<[email protected]> wrote:
Is there also a way to extract per parameter information (ex:
type) using
type deduction. Let me illustrate:
struct Toto( T1, T2 ) {
alias Key = T1;
alias Value = T2;
}
struct OuterToto( T ) if( isToto!T ) {
T.Key key;
T.Value value;
}
Imagine I would want that but without using inner aliases, is
this possible?
Sure, the U... part is accessible inside the static if. Just
define a
generic helper template:
struct Toto(First, Second)
{
}
template TemplateArguments(T)
{
static if (is(T _ : a!(Args), alias a, Args...))
alias TemplateArguments = Args;
else
alias TemplateArguments = void;
}
template TemplateName(T)
{
static if (is(T _ : a!(Args), alias a, Args...))
alias TemplateName = a;
else
alias TemplateName = void;
}
void main(string[] args)
{
alias Type = Toto!(int, double);
writeln(TemplateArguments!(Type).stringof);
writeln(TemplateName!(Type).stringof);
alias T = TemplateName!(Type);
alias Swapped = T!(double, int); // And you can use T as a
template.
}
As you can see, you can even use the deduced template name.
YES, it works! I just didn't realized you could only use it
inside the static ifs, thanks for pointing that out!
isInstanceOf( alias Template, T ) is nice but lacks support for
expressions directly: but that ain't a big deal, example:
struct Pair( T1, T2 ) {...}
template isPair( alias T ) {
static if( is( T ) ) {
enum isPair = isInstanceOf!( Pair, T );
} else {
enum isPair = isInstanceOf!( Pair, typeof( T ) ); //Must add
this to support expressions.
}
}
//Returns the type of the first term of the pair.
template FirstType( alias T ) if( isPair!T ) {
static if( is( T _: Pair!Args, Args... ) ) {
alias FirstType = Args[ 0 ];
} else {
alias FirstType = FirstType!( typeof( T );
}
}
The D programming language ROCKS :).
