Subtyping of an enum
diniz
diniz at posteo.net
Mon Apr 15 14:11:05 UTC 2019
Le 15/04/2019 à 10:39, Anton Fediushin via Digitalmars-d-learn a écrit :
> This seems to work just fine for assigning and comparisons but passing Enum as a
> function argument does not work:
> ```
> void fun(Enum e) {}
>
> fun(Enum.foo);
> ---
> Error: function fun(Enum e) is not callable using argument types (internal)
> Cannot pass argument foo of type internal to parameter Enum e.
> ```
I don't understand why you just don't call fun with an Enum (struct) param,
since that is how fun is defined. This works by me (see call in main):
struct Enum {
private {
enum internal {
foo,
bar
}
internal m_enum;
}
this (internal i) { m_enum = i; }
alias m_enum this;
string toString() {
switch (this.m_enum) {
case internal.foo : return "FOO" ;
case internal.bar : return "BAR" ;
default : assert(0) ;
}
}
}
void fun (Enum e) {
writeln(e) ;
}
void main() {
auto e = Enum(Enum.foo) ;
fun(e) ; // -> "FOO"
}
[And I wouldn't make the enum (little e) private, this just risks complicating
code, also eg in testing, I would just not export it.]
--
diniz {la vita e estranj}
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