On 03/03/2011 05:56 AM, Peter Lundgren wrote:
Where can I go to learn about parameterized structs? I can't seem to find any
literature on the subject. In particular, what are you allowed to use as a
parameter? I would like to define a struct like so:
struct MyStruct(T, T[] a) {
...
}
but I receive the following error:
Error: arithmetic/string type expected for value-parameter, not T[]
Are arrays not allowed?
Finally managed to do it, I guess :-)
============================
bool[E] set (E : E[]) (E[] elements) {
bool[E] set;
foreach (element ; elements)
set[element] = true;
return set;
}
struct String (C : C[], alias characters) {
alias typeof(characters) S;
//~ alias ElementType!S C; // BUG! returns dchar
bool[C] klass = null;
private C[] s;
this (S s) {
this.klass = set!S(characters);
this.def(s);
}
void def (S s = null) {
if (s.length == 0) {
this.s = s;
return;
}
foreach (ch ; s) {
if (ch !in this.klass) {
auto message = format(
"'%s' not in allowed class of characters"
, ch);
throw new Exception(message);
}
}
this.s = s;
}
string toString () {
return format("String!(%s,\"%s\")(\"%s\")",
S.stringof, characters, this.s);
}
}
unittest {
auto s = String!(string, "abcde")("");
writeln(s);
s.def("eca");
writeln(s);
s = String!(string, "abcde")("ace");
writeln(s);
s = String!(string, "abcde")("fgh"); // --> error
writeln(s);
}
============================
Some notes:
* set is here to speed up character lookup among allowed klass (else, O(N) in
array).
* C: C[] in struct template is redondant, since C[] is typeof(characters). It
is only needed to declare the set 'klass', because of a bug: ElementType!string
returns dchar!!! Thus, it is would not be possible, I guess, to declare klass's
type in the struct definition.
* You must pass an init string (even if "") to call this() and construct klass.
Because of another bug: there cannot be parameter-less constructors for
structs. Also, set cannot be defined on toplevel of the struct def
auto klass = set!S(characters);
because it's not a constant according to dmd. (It is, in fact). Thus, I guess
we must construct it inside this().
Denis
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