Get struct template types
Hi,
given a struct like so:
struct S(alias N, T) {...}
is there a way to get the template parameters of S? Something
like:
S.typetuple[0] == N,
S.typetuple[1] == T
I've had a look at std.typecons and std.typetuple but I don't see
what I'm missing something and cannot see a way to do the above.
Thanks,
ed
Re: Get struct template types
On Tuesday, 4 February 2014 at 09:30:22 UTC, ed wrote:
Hi,
given a struct like so:
struct S(alias N, T) {...}
is there a way to get the template parameters of S? Something
like:
S.typetuple[0] == N,
S.typetuple[1] == T
I've had a look at std.typecons and std.typetuple but I don't
see what I'm missing something and cannot see a way to do the
above.
Thanks,
ed
typeof(N).stringof will return type of N as string
for details read http://dlang.org/expression.html
Re: Get struct template types
On Tuesday, 4 February 2014 at 09:39:48 UTC, evilrat wrote:
On Tuesday, 4 February 2014 at 09:30:22 UTC, ed wrote:
Hi,
given a struct like so:
struct S(alias N, T) {...}
is there a way to get the template parameters of S? Something
like:
S.typetuple[0] == N,
S.typetuple[1] == T
I've had a look at std.typecons and std.typetuple but I don't
see what I'm missing something and cannot see a way to do the
above.
Thanks,
ed
typeof(N).stringof will return type of N as string
for details read http://dlang.org/expression.html
oops sorry, it's for another people.
what are you trying to achieve? when passing types as template
args it is still types, so again typeof should give you type for
variables(in such cases there is typeof), otherwise type is type.
also, afaik it is not possible to store types in tuple, but i
think you can store variables in tuple and retrieve their types
at runtime
Re: Get struct template types
On Tuesday, 4 February 2014 at 09:58:53 UTC, ed wrote:
On Tuesday, 4 February 2014 at 09:46:01 UTC, evilrat wrote:
On Tuesday, 4 February 2014 at 09:39:48 UTC, evilrat wrote:
On Tuesday, 4 February 2014 at 09:30:22 UTC, ed wrote:
Hi,
given a struct like so:
struct S(alias N, T) {...}
is there a way to get the template parameters of S?
Something like:
S.typetuple[0] == N,
S.typetuple[1] == T
I've had a look at std.typecons and std.typetuple but I
don't see what I'm missing something and cannot see a way to
do the above.
Thanks,
ed
typeof(N).stringof will return type of N as string
for details read http://dlang.org/expression.html
oops sorry, it's for another people.
what are you trying to achieve? when passing types as template
args it is still types, so again typeof should give you type
for variables(in such cases there is typeof), otherwise type
is type. also, afaik it is not possible to store types in
tuple, but i think you can store variables in tuple and
retrieve their types at runtime
I am trying to set up an isS, isSOfN or isSOfT so I can create
functions that allow restricted types of S based on all, or
only one of the template parameters.
Like so (pseudo-D code)
---
struct S(alias N, T) {}
//
// Hopefully it is clear what I am trying to do here
enum isSOfN = template(alias N,STYPE) {
static assert(N == STYPET.typetuple[0]);
}
enum isSOfT = template(T,STYPE) {
static assert(T == STYPET.typetuple[1]);
}
//
void f(T)(T t) if(isSOfN!(3, T)) { // allow S with N=3 and any
T (see below)
}
...
...
auto s3i = S!(3,int);
auto s3f = S!(3,float);
s3i.f(); // Succeeds
s3f.f(); // Succeeds
auto S4i = S!(4,int);
s4i.f(); // compile time error
--
I'm looking into T.stringof now, I might be able to get it
working with some compile-time string magic of D :)
If this is a bad way to go about it please let me know. I'm
trying to learn idiomatic D as I go.
Thanks,
ed
for this simple case static if is pretty straightforward, but
then if only purpose is to construct type it is better use
regular generic function and typecons i think.
--
import std.stdio;
struct S(alias N, T)
{
T x;
void f()
{
static if(N==3)
{
writeln(n = 3, type = , T.stringof);
}
else static if (N == 2)
{
writeln(n = 2, type = , T.stringof);
}
else
static assert(0, NO!);
}
}
void main()
{
S!(3, int) a; // ok
S!(2, float) b; // ok
S!(4, double) c; // oops
a.f();
b.f();
}
--
Re: Get struct template types
On Tuesday, 4 February 2014 at 09:30:22 UTC, ed wrote:
Hi,
given a struct like so:
struct S(alias N, T) {...}
is there a way to get the template parameters of S? Something
like:
S.typetuple[0] == N,
S.typetuple[1] == T
I've had a look at std.typecons and std.typetuple but I don't
see what I'm missing something and cannot see a way to do the
above.
Thanks,
ed
Use type deduction:
---
struct S(size_t n, T) {}
enum isS(T) = is(T == S!(n, U), size_t n, U);
template isS(T, size_t n)
{
static if(is(T == S!(n2, U), size_t n2, U))
enum isS = n == n2;
else
enum isS = false;
}
alias MyS = S!(3, float);
static assert(isS!MyS);
static assert(isS!(MyS, 3));
static assert(is(MyS == S!(3, float)));
---
