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Add support for self-referential types using "This" placeholder.

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This commit is contained in:
Sönke Ludwig 2019-02-22 17:34:08 +01:00
parent 3fc701edba
commit f4b621963c
1 changed files with 64 additions and 28 deletions
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92
source/taggedalgebraic/taggedunion.d
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@ -578,45 +578,81 @@ private string pascalCase(string camel_case)
return camel_case[0].toUpper ~ camel_case[1 .. $];
}
static if (__VERSION__ >= 2072) {
/** Maps a kind enumeration value to the corresponding field type.
/** Maps a kind enumeration value to the corresponding field type.
`kind` must be a value of the `TaggedAlgebraic!T.Kind` enumeration.
*/
template TypeOf(alias kind)
if (is(typeof(kind) == enum))
{
static if (isInstanceOf!(UnionFieldEnum, typeof(kind))) {
import std.traits : FieldTypeTuple, TemplateArgsOf;
alias U = TemplateArgsOf!(typeof(kind));
alias TypeOf = FieldTypeTuple!U[kind];
} else {
alias Types = UnionKindTypes!(typeof(kind));
alias uda = AliasSeq!(__traits(getAttributes, kind));
static if (uda.length == 0) alias TypeOf = void;
else alias TypeOf = uda[0];
}
`kind` must be a value of the `TaggedAlgebraic!T.Kind` enumeration.
*/
template TypeOf(alias kind)
if (is(typeof(kind) == enum))
{
import std.traits : FieldTypeTuple, TemplateArgsOf;
import std.typecons : ReplaceType;
static if (isInstanceOf!(UnionFieldEnum, typeof(kind))) {
alias U = TemplateArgsOf!(typeof(kind));
alias FT = FieldTypeTuple!U[kind];
} else {
alias U = typeof(kind);
alias Types = UnionKindTypes!(typeof(kind));
alias uda = AliasSeq!(__traits(getAttributes, kind));
static if (uda.length == 0) alias FT = void;
else alias FT = uda[0];
}
///
unittest {
static struct S {
int a;
string b;
string c;
}
alias TU = TaggedUnion!S;
alias TypeOf = ReplaceType!(This, U, FT);
}
static assert(is(TypeOf!(TU.Kind.a) == int));
static assert(is(TypeOf!(TU.Kind.b) == string));
static assert(is(TypeOf!(TU.Kind.c) == string));
///
unittest {
static struct S {
int a;
string b;
string c;
}
alias TU = TaggedUnion!S;
static assert(is(TypeOf!(TU.Kind.a) == int));
static assert(is(TypeOf!(TU.Kind.b) == string));
static assert(is(TypeOf!(TU.Kind.c) == string));
}
unittest {
struct S {
TaggedUnion!This[] test;
}
alias TU = TaggedUnion!S;
TypeOf!(TU.Kind.test) a;
static assert(is(TypeOf!(TU.Kind.test) == TaggedUnion!S[]));
}
/// Convenience type that can be used for union fields that have no value (`void` is not allowed).
struct Void {}
/** Special type used as a placeholder for `U` within the definition of `U` to
enable self-referential types.
Note that this is recognized only if used as the first argument to a
template type.
*/
struct This { Void nothing; }
///
unittest {
union U {
TaggedUnion!This[] list;
int number;
string text;
}
alias Node = TaggedUnion!U;
auto n = Node([Node(12), Node("foo")]);
assert(n.isList);
assert(n.listValue == [Node(12), Node("foo")]);
}
private template UnionFieldEnum(U)
{
static if (is(U == enum)) alias UnionFieldEnum = U;