digitalmars.D.learn - Detecting array type without template specialization?
- Jarrett Billingsley (42/42) May 09 2006 Say I want a template to do different things if it's passed an array ver...
- Sean Kelly (15/70) May 09 2006 template isArrayType( T ) { const bool isArrayType = false; }
- Jarrett Billingsley (4/16) May 09 2006 Oh cool.
- Bruno Medeiros (7/83) May 12 2006 It is kinda odd that the 'is expression' doesn't feature arrays as one
Say I want a template to do different things if it's passed an array versus
a non-array type. I can do this easily with template specialization:
template Spoon(T)
{
void knife()
{
writefln("single");
}
}
template Spoon(T : T[])
{
void knife()
{
writefln("array");
}
}
...
mixin Spoon!(int) i;
mixin Spoon!(int[]) a;
i.knife();
a.knife();
That prints
single
array
As I'd like it to.
That works great, but what if I'm writing a much larger class, where most of
the functionality would be the same between the array and non-array
versions, and I only want to change, say, one function to work differently
for arrays? It would be redundant and cumbersome to have to copy most of
the contents of one template to the other.
Something like this can be done for classes versus non-classes:
template Spoon(T)
{
void knife()
{
static if(is(T : Object))
writefln("class");
else
writefln("non-class");
}
}
But is there any way to do this for array types?
May 09 2006
Jarrett Billingsley wrote:
Say I want a template to do different things if it's passed an array versus
a non-array type. I can do this easily with template specialization:
template Spoon(T)
{
void knife()
{
writefln("single");
}
}
template Spoon(T : T[])
{
void knife()
{
writefln("array");
}
}
...
mixin Spoon!(int) i;
mixin Spoon!(int[]) a;
i.knife();
a.knife();
That prints
single
array
As I'd like it to.
That works great, but what if I'm writing a much larger class, where most of
the functionality would be the same between the array and non-array
versions, and I only want to change, say, one function to work differently
for arrays? It would be redundant and cumbersome to have to copy most of
the contents of one template to the other.
Something like this can be done for classes versus non-classes:
template Spoon(T)
{
void knife()
{
static if(is(T : Object))
writefln("class");
else
writefln("non-class");
}
}
But is there any way to do this for array types?
template isArrayType( T ) { const bool isArrayType = false; }
template isArrayType( T : T[] ) { const bool isArrayType = true; }
template Spoon( T )
{
void knife()
{
static if( isArrayType( T ) )
writefln( "array" );
else
writefln( "not array" );
}
}
This sort of thing is why I created std.traits in Ares.
Sean
May 09 2006
"Jarrett Billingsley" <kb3ctd2 yahoo.com>
"Sean Kelly" <sean f4.ca> wrote in message
news:e3qub9$odc$1 digitaldaemon.com...
template isArrayType( T ) { const bool isArrayType = false; }
template isArrayType( T : T[] ) { const bool isArrayType = true; }
template Spoon( T )
{
void knife()
{
static if( isArrayType( T ) )
writefln( "array" );
else
writefln( "not array" );
}
}
Oh cool.
Thanks :)
May 09 2006
Sean Kelly wrote:Jarrett Billingsley wrote:It is kinda odd that the 'is expression' doesn't feature arrays as one of it's testable archetypes (it has: typedef struct union class interface enum function delegate) -- Bruno Medeiros - CS/E student http://www.prowiki.org/wiki4d/wiki.cgi?BrunoMedeiros#DSay I want a template to do different things if it's passed an array versus a non-array type. I can do this easily with template specialization: template Spoon(T) { void knife() { writefln("single"); } } template Spoon(T : T[]) { void knife() { writefln("array"); } } ... mixin Spoon!(int) i; mixin Spoon!(int[]) a; i.knife(); a.knife(); That prints single array As I'd like it to. That works great, but what if I'm writing a much larger class, where most of the functionality would be the same between the array and non-array versions, and I only want to change, say, one function to work differently for arrays? It would be redundant and cumbersome to have to copy most of the contents of one template to the other. Something like this can be done for classes versus non-classes: template Spoon(T) { void knife() { static if(is(T : Object)) writefln("class"); else writefln("non-class"); } } But is there any way to do this for array types?template isArrayType( T ) { const bool isArrayType = false; } template isArrayType( T : T[] ) { const bool isArrayType = true; } template Spoon( T ) { void knife() { static if( isArrayType( T ) ) writefln( "array" ); else writefln( "not array" ); } } This sort of thing is why I created std.traits in Ares. Sean
May 12 2006