[Issue 9924] New: Handy enum accessors
d-bugmail at puremagic.com
d-bugmail at puremagic.com
Thu Apr 11 17:20:50 PDT 2013
http://d.puremagic.com/issues/show_bug.cgi?id=9924
Summary: Handy enum accessors
Product: D
Version: D2
Platform: All
OS/Version: All
Status: NEW
Severity: enhancement
Priority: P2
Component: Phobos
AssignedTo: nobody at puremagic.com
ReportedBy: bearophile_hugs at eml.cc
--- Comment #0 from bearophile_hugs at eml.cc 2013-04-11 17:20:49 PDT ---
To better use enums I suggest to add to Phobos four small templates/functions
like this (similar things are builtins in Ada):
import std.conv: text;
import std.traits: EnumMembers;
template FirstMember(E) if (is(E == enum)) {
enum FirstMember = EnumMembers!E[0];
}
template LastMember(E) if (is(E == enum)) {
enum LastMember = EnumMembers!E[$ - 1];
}
E predMember(E)(E e) /*pure nothrow*/ if (is(E == enum))
in {
assert(e != FirstMember!E);
} body {
switch (e) {
foreach (i, e2; EnumMembers!E[1 .. $])
mixin("case E." ~ text(cast(E)e2) ~ ": return E."
~ text(cast(E)(EnumMembers!E[i])) ~ ";");
default: assert(0);
}
}
E nextMember(E)(E e) /*pure nothrow*/ if (is(E == enum))
in {
assert(e != LastMember!E);
} body {
switch (e) {
foreach (i, e2; EnumMembers!E[0 .. $ - 1])
mixin("case E." ~ text(cast(E)e2) ~ ": return E."
~ text(cast(E)(EnumMembers!E[i + 1])) ~ ";");
default: assert(0);
}
}
void main() { // Demo -----------------------
import std.stdio;
enum Choice { rock, paper, scissors }
static Choice whatBeats(in Choice ch) /*pure nothrow*/ {
if (ch == LastMember!Choice)
return FirstMember!Choice;
else
return nextMember(ch);
}
foreach (e; [EnumMembers!Choice])
writeln(e, " ", whatBeats(e));
writeln(predMember(Choice.paper));
writeln(predMember(Choice.scissors));
writeln(nextMember(Choice.rock));
writeln(nextMember(Choice.paper));
}
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