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version 2.110.0

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Template std.typecons.unwrap

Supports structural based typesafe conversion.

template unwrap(Target);
alias unwrap(Target) = unwrap!(Unqual!Target);

If Source has structural conformance with the interface Targets, wrap creates an internal wrapper class which inherits Targets and wraps the src object, then returns it.

unwrap can be used to extract objects which have been wrapped by wrap.

Template unwrap

Contained Functions

NameDescription
unwrap
unwrap

Alias unwrap

Example

interface Quack
{
    int quack();
    @property int height();
}
interface Flyer
{
    @property int height();
}
class Duck : Quack
{
    int quack() { return 1; }
    @property int height() { return 10; }
}
class Human
{
    int quack() { return 2; }
    @property int height() { return 20; }
}

Duck d1 = new Duck();
Human h1 = new Human();

interface Refleshable
{
    int reflesh();
}

// does not have structural conformance
static assert(!__traits(compiles, d1.wrap!Refleshable));
static assert(!__traits(compiles, h1.wrap!Refleshable));

// strict upcast
Quack qd = d1.wrap!Quack;
assert(qd is d1);
assert(qd.quack() == 1);    // calls Duck.quack
// strict downcast
Duck d2 = qd.unwrap!Duck;
assert(d2 is d1);

// structural upcast
Quack qh = h1.wrap!Quack;
assert(qh.quack() == 2);    // calls Human.quack
// structural downcast
Human h2 = qh.unwrap!Human;
assert(h2 is h1);

// structural upcast (two steps)
Quack qx = h1.wrap!Quack;   // Human -> Quack
Flyer fx = qx.wrap!Flyer;   // Quack -> Flyer
assert(fx.height == 20);    // calls Human.height
// structural downcast (two steps)
Quack qy = fx.unwrap!Quack; // Flyer -> Quack
Human hy = qy.unwrap!Human; // Quack -> Human
assert(hy is h1);
// structural downcast (one step)
Human hz = fx.unwrap!Human; // Flyer -> Human
assert(hz is h1);

Example

import std.traits : FunctionAttribute, functionAttributes;
interface A { int run(); }
interface B { int stop(); @property int status(); }
class X
{
    int run() { return 1; }
    int stop() { return 2; }
    @property int status() { return 3; }
}

auto x = new X();
auto ab = x.wrap!(A, B);
A a = ab;
B b = ab;
writeln(a.run()); // 1
writeln(b.stop()); // 2
writeln(b.status); // 3
static assert(functionAttributes!(typeof(ab).status) & FunctionAttribute.property);

Authors

Andrei Alexandrescu, Bartosz Milewski, Don Clugston, Shin Fujishiro, Kenji Hara

License

Boost License 1.0.