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Merge pull request #42 from schveiguy/addvisit

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Add forwarder for visit and tryVisit from TaggedUnion to TaggedAlgebraic
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Sönke Ludwig 2019-11-30 16:24:36 +01:00 committed by GitHub
parent a6d7a8b2ad 4bcd34d417
commit 44a2b970af
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81
source/taggedalgebraic/taggedalgebraic.d
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@ -798,6 +798,87 @@ unittest {
});
}
/** Forwards visit functionality from taggedunion.
A visitor can have one of three forms:
$(UL
$(LI function or delegate taking a single typed parameter)
$(LI function or delegate taking no parameters)
$(LI function or delegate template taking any single parameter)
)
....
*/
template visit(VISITORS...)
if (VISITORS.length > 0)
{
auto visit(U)(auto ref TaggedAlgebraic!U ta)
{
return taggedalgebraic.taggedunion.visit!VISITORS(ta.m_union);
}
}
unittest {
// repeat test from TaggedUnion
union U {
Void none;
int count;
float length;
}
TaggedAlgebraic!U u;
//
static assert(is(typeof(u.visit!((int) {}, (float) {}, () {}))));
static assert(is(typeof(u.visit!((_) {}, () {}))));
static assert(is(typeof(u.visit!((_) {}, (float) {}, () {}))));
static assert(is(typeof(u.visit!((float) {}, (_) {}, () {}))));
static assert(!is(typeof(u.visit!((_) {})))); // missing void handler
static assert(!is(typeof(u.visit!(() {})))); // missing value handler
static assert(!is(typeof(u.visit!((_) {}, () {}, (string) {})))); // invalid typed handler
static assert(!is(typeof(u.visit!((int) {}, (float) {}, () {}, () {})))); // duplicate void handler
static assert(!is(typeof(u.visit!((_) {}, () {}, (_) {})))); // duplicate generic handler
static assert(!is(typeof(u.visit!((int) {}, (float) {}, (float) {}, () {})))); // duplicate typed handler
// TODO: error out for superfluous generic handlers
//static assert(!is(typeof(u.visit!((int) {}, (float) {}, () {}, (_) {})))); // superfluous generic handler
}
/** Forwards tryVisit functionality from taggedunion.
The same as `visit`, except that failure to handle types is checked at runtime.
Instead of failing to compile, `tryVisit` will throw an `Exception` if none
of the handlers is able to handle the value contained in `ta`.
*/
template tryVisit(VISITORS...)
if (VISITORS.length > 0)
{
auto tryVisit(U)(auto ref TaggedAlgebraic!U ta)
{
return taggedalgebraic.taggedunion.tryVisit!VISITORS(ta.m_union);
}
}
// repeat from TaggedUnion
unittest {
import std.exception : assertThrown;
union U {
int number;
string text;
}
alias TA = TaggedAlgebraic!U;
auto ta = TA(42);
ta.tryVisit!((int n) { assert(n == 42); });
assertThrown(ta.tryVisit!((string s) { assert(false); }));
}
/// User-defined attibute to disable `opIndex` forwarding for a particular tagged union member.
@property auto disableIndex() { assert(__ctfe, "disableIndex must only be used as an attribute."); return DisableOpAttribute(OpKind.index, null); }