TaggedUnion

Implements a generic tagged union type.

This struct takes a union or struct declaration as an input and builds an algebraic data type from its fields, using an automatically generated Kind enumeration to identify which field of the union is currently used. Multiple fields with the same value are supported.

For each field defined by U a number of convenience members are generated. For a given field "foo", these fields are:

static foo(value) - returns a new tagged union with the specified value
isFoo - equivalent to kind == Kind.foo
setFoo(value) - equivalent to set!(Kind.foo)(value)
getFoo - equivalent to get!(Kind.foo)

template TaggedUnion (

) if (

is(U == union) ||

is(U == struct)

is(U == enum)

) {

struct TaggedUnion;

}

Members

Structs

TaggedUnion struct TaggedUnion: Undocumented in source.

Examples

union Kinds {
	int count;
	string text;
}
alias TU = TaggedUnion!Kinds;

// default initialized to the first field defined
TU tu;
assert(tu.kind == TU.Kind.count);
assert(tu.isCount); // qequivalent to the line above
assert(!tu.isText);
assert(tu.value!(TU.Kind.count) == int.init);

// set to a specific count
tu.setCount(42);
assert(tu.isCount);
assert(tu.countValue == 42);
assert(tu.value!(TU.Kind.count) == 42);
assert(tu.value!int == 42); // can also get by type
assert(tu.countValue == 42);

// assign a new tagged algebraic value
tu = TU.count(43);

// test equivalence with other tagged unions
assert(tu == TU.count(43));
assert(tu != TU.count(42));
assert(tu != TU.text("hello"));

// modify by reference
tu.countValue++;
assert(tu.countValue == 44);

// set the second field
tu.setText("hello");
assert(!tu.isCount);
assert(tu.isText);
assert(tu.kind == TU.Kind.text);
assert(tu.textValue == "hello");

// unique types can also be directly constructed
tu = TU(12);
assert(tu.countValue == 12);
tu = TU("foo");
assert(tu.textValue == "foo");

TaggedUnion

Members

Structs

Examples

Meta

Source