static if with constant value
Bill Baxter
dnewsgroup at billbaxter.com
Wed Dec 13 16:11:52 PST 2006
Doh, I figured out why it does what it does now. I had assumed that
floats and doubles didn't have .re and .im properties, so that that
would cause the is() check to fail.
So what's a better way to check for complexity of a type?
I'd rather not have to list every complex type explicitly. It's ugly
for one, but more importantly it precludes recognizing user types as
complex-like.
Maybe this is close enough?
static if( is(T:cfloat) || is(T:cdouble) || is(T:creal) ) {...}
--bb
Bill Baxter wrote:
> I can't understand why the little program below outputs what it does.
> It seems like static if (constant) works in some cases but not others.
> Is this just a bug?
>
> ----
> import std.stdio : writef, writefln;
>
> template is_complex(T)
> {
> static if (is(typeof(T.init.re)) && is(typeof(T.init.im))) {
> const bool is_complex = true;
> } else {
> const bool is_complex = false;
> }
> }
> template float_for_type(T)
> {
> static if ( is_complex!(T) ) {
> alias typeof(T.init.re) float_for_type;
> } else {
> alias T float_for_type;
> }
> }
>
> void print_complex(T)(T* arg)
> {
> static const bool cplx = is_complex!(T);
> writefln("print_complex: Type: %s, is_complex? ", typeid(T), cplx);
> static if ( is_complex!(T) ) {
> writefln("print_complex: static if is_complex? true");
> } else {
> writefln("print_complex: static if is_complex? false");
> }
> }
>
>
> void main()
> {
> float f;
> cfloat c;
> double d;
> cdouble z;
> writefln("main: %s made from %s", typeid(typeof(f)),
> typeid(float_for_type!(typeof(f)))); print_complex(&f);
> writefln("main: %s made from %s", typeid(typeof(c)),
> typeid(float_for_type!(typeof(c)))); print_complex(&c);
> writefln("main: %s made from %s", typeid(typeof(d)),
> typeid(float_for_type!(typeof(d)))); print_complex(&d);
> writefln("main: %s made from %s", typeid(typeof(z)),
> typeid(float_for_type!(typeof(z)))); print_complex(&z);
> }
> ----
>
>
> Here's what it outputs for me with DMD:
>
> main: float made from float
> print_complex: Type: float, is_complex? true
> print_complex: static if is_complex? true
> main: cfloat made from float
> print_complex: Type: cfloat, is_complex? true
> print_complex: static if is_complex? true
> main: double made from double
> print_complex: Type: double, is_complex? true
> print_complex: static if is_complex? true
> main: cdouble made from double
> print_complex: Type: cdouble, is_complex? true
> print_complex: static if is_complex? true
>
>
> In float_for_type!(T), is_complex!(T) works, but in print_complex it
> does not for some reason (it always evaluates to true). Can anyone
> explain this behavior?
>
> --bb
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