On Sunday, 14 January 2018 at 22:07:22 UTC, Marc wrote:
thanks, can i use it at compile time as well?
enum isMutableString(string field) =
is(typeof(__traits(getMember, >C, field)) == string);
static foreach(field; [FieldNameTuple!C].filter!(f =>
isMutableString!(f))) {
writeln(field);
}
You're mixing compile-time and run-time logic here in a way that
D doesn't allow. In particular, isMutableString requires the
passed string to be a compile-time constant, and filter works on
run-time values.
There are a few different ways to resolve this. First, std.meta
has the Filter template, which behaves much in the same way as
std.algorithm.filter, but with compile-time tuples:
static foreach (field; Filter!(isMutableString,
FieldNameTuple!C)) {
writeln(field);
}
The other option is to rewrite isMutableString to work with
run-time values:
bool isMutableString(string field) {
switch (field) {
foreach (cField; FieldNameTuple!C) {
case cField:
return is(typeof(__traits(getMember, C, cField))
== string);
}
default:
return false;
}
}
static foreach(field; [FieldNameTuple!C].filter!(f =>
isMutableString(f))) {
writeln(field);
}
Both of these give the same output, and should be what you want.
--
Simen
