### Re: Check Instance of Template for Parameter Type/Value

```
On Monday, 19 October 2015 at 14:51:29 UTC, Stewart Moth wrote:
I'm working with a library that has template structs of
mathematical vectors that can sometimes be the type of an array
I'm passing to a function.

The definition of the struct is like this:

struct Vector(type, int dimension_){ ... }

Where type is going to be an int/float/etc and dimension_ is
2/3/4.

I could write a bunch of functions for each case, but I'd
rather not... I'd like to use something like the following:

void foo(T)(Array!T array){
if(isInstanceOf!(Vector, T)){
//get type of T or check it
//test if dimension_ is 2 or 3 or 4
...
} else {
//Non-vector stuff
...
}
}

But to do that I need to check that parameters of T as if it
were an instantiated instance of Vector and I'm not sure how to
accomplish that... Can anyone help me out with what I need to
do?

I'm not sure if this is exactly what you're after, but with the
traits shown below you should be able to perform the following
compile time checks.

---
void foo(T)(T v){

static if(isVec!(T)){ } // Vec of any type and size
static if(isVec!(T, int)){ } // Vec of type 'int' but any size
static if(isVec!(T, 3)){ } // Vec of size 3 but any type
static if(isVec!(T, 3, int)){ } // Vec of size 3 and type
'int'

}
---

Traits impl:
(this is from memory with no D compiler around so excuse any
typos)

---

struct Vec(size_t Dim, Type) {} // Vector template parms
dimension and type.

/**
* Is V a Vec of any element type and any size
*/
template isVec(V)
{
enum isVec = is(Unqual!V == Vec!(n, U), size_t n, U);
}
///
unittest {
mixin(UT_start);
static assert(isVec!(Vec!(2,float)));
static assert(isVec!(Vec!(4,int)));
mixin(UT_scopeExit);
}

/**
*  Is V a Vec of a specific size but any type.
*/
template isVec(V, size_t n)
{
static if(is(Unqual!V == Vec!(n2, U), size_t n2, U))
enum isVec = n == n2;
else
enum isVec = false;
}

/**
*  Is V a Vec of any size and specific type T.
*/
template isVec(V, T)
{
static if(is(Unqual!V == Vec!(n, U), size_t n, U))
enum isVec = is(T == U);
else
enum isVec = false;
}
///
unittest {
mixin(UT_start);
static assert(isVec!(Vec!(2,int), int));
static assert(isVec!(Vec!(3,int), int));
static assert(!isVec!(Vec!(2,int), float));
static assert(!isVec!(Vec!(3,int), float));
mixin(UT_scopeExit);
}

/**
*  Is V a Vec of specific size N and type T
*/
template isVec(V,size_t N,T)
{
enum isVec = is(Unqual!V == Vec!(N,T));
}
///
unittest {
mixin(UT_start);
static assert(isVec!(Vec!(2,int), 2, int));
static assert(!isVec!(Vec!(2,int), 3, int));
static assert(!isVec!(Vec!(2,int), 2, float));
static assert(!isVec!(Vec!(2,int), 3, float));
mixin(UT_scopeExit);
}
---

Cheers,
Stew

```

### Check Instance of Template for Parameter Type/Value

```I'm working with a library that has template structs of
mathematical vectors that can sometimes be the type of an array
I'm passing to a function.

The definition of the struct is like this:

struct Vector(type, int dimension_){ ... }

Where type is going to be an int/float/etc and dimension_ is
2/3/4.

I could write a bunch of functions for each case, but I'd rather
not... I'd like to use something like the following:

void foo(T)(Array!T array){
if(isInstanceOf!(Vector, T)){
//get type of T or check it
//test if dimension_ is 2 or 3 or 4
...
} else {
//Non-vector stuff
...
}
}

But to do that I need to check that parameters of T as if it were
an instantiated instance of Vector and I'm not sure how to
accomplish that... Can anyone help me out with what I need to do?

```

### Re: Check Instance of Template for Parameter Type/Value

```On Monday, October 19, 2015 04:51 PM, Stewart Moth wrote:

> struct Vector(type, int dimension_){ ... }
>
> Where type is going to be an int/float/etc and dimension_ is
> 2/3/4.
>
> I could write a bunch of functions for each case, but I'd rather
> not... I'd like to use something like the following:
>
> void foo(T)(Array!T array){
>  if(isInstanceOf!(Vector, T)){
>  //get type of T or check it
>  //test if dimension_ is 2 or 3 or 4
>  ...
>  } else {
>  //Non-vector stuff
>  ...
>  }
> }
>
> But to do that I need to check that parameters of T as if it were
> an instantiated instance of Vector and I'm not sure how to
> accomplish that... Can anyone help me out with what I need to do?

You can use std.traits.TemplateArgsOf:

static if(isInstanceOf!(Vector, T)){ /* note: must be a static if */
enum dimensions = TemplateArgsOf!T[1];
static if(dimensions == 2) {...}
}

```

### Re: Check Instance of Template for Parameter Type/Value

```On Mon, 19 Oct 2015 14:51:28 +, Stewart Moth wrote:

> I'm working with a library that has template structs of mathematical
> vectors that can sometimes be the type of an array I'm passing to a
> function.
>
> The definition of the struct is like this:
>
> struct Vector(type, int dimension_){ ... }
>
> Where type is going to be an int/float/etc and dimension_ is 2/3/4.
>
> I could write a bunch of functions for each case, but I'd rather not...
> I'd like to use something like the following:
>
> void foo(T)(Array!T array){
>  if(isInstanceOf!(Vector, T)){
>  //get type of T or check it //test if dimension_ is 2 or 3 or 4
>  ...
>  } else {
>  //Non-vector stuff ...
>  }
> }
>
> But to do that I need to check that parameters of T as if it were an
> instantiated instance of Vector and I'm not sure how to accomplish
> that... Can anyone help me out with what I need to do?

Pattern matching!

void foo(ArrayT : Array!VectorT, VectorT : Vector!(T, dimension), T, int
dimension)(ArrayT arr)
{
static if (dimension >= 2 && dimension <= 4)
{

} else {

}
}

```