Distinguishing between const and non-const variable in a template?
mario pernici
mario.pernici at mi.infn.it
Thu Feb 22 06:01:23 PST 2007
renoX Wrote:
> Hello,
>
> I'm trying to improve format string by allowing the format
> " ... %{x} ...", my problem is that when I give a non-const char[]
> parameter in
> mixin(Putf!(foo));
>
> then the template fail..
>
> How can I reliably detect in a template if the parameter is a constant
> or not?
>
> My goal is:
> if the parameter isn't a const char[]: leave its name unchanged so that
> it's parsed by the writef at runtime, if it is a const char[]: parse it
> myself with the new syntax.
>
> Regards,
> renoX
>
> template FindChar(char[] A, char B) {
> static if (A.length == 0) {
> const int FindChar = -1;
> } else static if (A[0] == B) {
> const int FindChar = 0;
> } else static if (-1 == FindChar!(A[1..$], B)) {
> const int FindChar = -1;
> } else {
> const int FindChar = 1 + FindChar!(A[1..$], B);
> }
> }
>
> template FmtString(char[] F, A...)
> {
> static if (F.length == 0)
> static if (A.length)
> const char[] FmtString = "\"," ~ Fmt!(A);
> else
> const char[] FmtString = "\"";
> else static if (F.length == 1)
> static if (A.length)
> const char[] FmtString = F[0] ~ "\"," ~ Fmt!(A);
> else
> const char[] FmtString = F[0] ~ "\"";
> else static if (F[0..2] == "%%")
> const char[] FmtString = "%%" ~ FmtString!(F[2..$], A);
> else static if (F[0..2] == "%{")
> {
> // get the variable name between %{ and }
> static if (FindChar!(F, '}') <= 2)
> static assert(0, "format %{} incorrect in '" ~ F ~ "'");
> const char[] FmtString = "%s\"," ~ F[2..FindChar!(F,'}')] ~ ",\"" ~
> FmtString!(F[1+FindChar!(F,'}')..$], A);
> }
> else
> const char[] FmtString = F[0] ~ FmtString!(F[1..$], A);
> }
>
> template Fmt(A...)
> {
> //static assert(0, cast(char*)A[0]);
> static if (A.length == 0)
> const char[] Fmt = "";
> else static if (is(typeof(A[0]) : char[]))
> const char[] Fmt = "\"" ~ FmtString!(A[0], A[1..$]);
> else static if (A.length == 1)
> const char[] Fmt = A[0].stringof;
> else
> const char[] Fmt = A[0].stringof ~ "," ~ Fmt!(A[1..$]);
> }
>
> template Putf(A...)
> {
> const char[] Putf = "writef(" ~ Fmt!(A) ~ ");";
> }
Maybe you can use something like this
const char[] s = "ab";
static if(is(typeof(&s))) {
writefln(s, " not constant");
}
else {
static if(is(typeof(s))) {
writefln(s, " constant");
}
}
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