On 2012-11-06, 16:20, Joseph Rushton Wakeling wrote:
Suppose that I have two struct templates which take identical parameter
lists:
struct Foo(T1, T2, T3)
{
...
}
struct Bar(T1, T2, T3)
{
...
}
Now suppose that I have a Foo which has been instantiated with a given
set of parameters. Is there any way for me to say, "now instantiate a
Bar with the same parameters?"
The use-case I'm thinking of is a function something like this (somewhat
pseudo-code-y):
auto fooToBar(FooInstance f)
{
Bar!(f.T1, f.T2, f.T3) b;
// set values etc.
return b;
}
Of course the f.T1 notation is my fiction, but it gives the idea of what
is needed -- is there a means to extract and use template parameters in
this way? I assume something from std.traits but it's not entirely clear
what or how ...
In addition to Dan's answer, let me present a general solution:
template InstantiationInfo( T ) {
static if ( is( T t == U!V, alias U, V... ) ) {
alias U Template;
alias V Parameters;
} else {
static assert(false, T.stringof ~ " is not a template type
instantiation.");
}
}
With this, you can extract the parameters to a template
(InstantiationInfo!Foo.Parameters) or the template used
(InstantiationInfo!Foo.Template).
--
Simen
