mirror of https://github.com/adamdruppe/arsd.git
94 lines
2.7 KiB
D
94 lines
2.7 KiB
D
/++
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mvd stands for Multiple Virtual Dispatch. It lets you
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write functions that take any number of arguments of
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objects and match based on the dynamic type of each
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of them.
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---
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void foo(Object a, Object b) {} // 1
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void foo(MyClass b, Object b) {} // 2
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void foo(DerivedClass a, MyClass b) {} // 3
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Object a = new MyClass();
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Object b = new Object();
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mvd!foo(a, b); // will call overload #2
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---
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The return values must be compatible; [mvd] will return
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the least specialized static type of the return values
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(most likely the shared base class type of all return types,
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or `void` if there isn't one).
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All non-class/interface types should be compatible among overloads.
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Otherwise you are liable to get compile errors. (Or it might work,
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that's up to the compiler's discretion.)
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+/
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module arsd.mvd;
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import std.traits;
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/// This exists just to make the documentation of [mvd] nicer looking.
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alias CommonReturnOfOverloads(alias fn) = CommonType!(staticMap!(ReturnType, __traits(getOverloads, __traits(parent, fn), __traits(identifier, fn))));
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/// See details on the [arsd.mvd] page.
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CommonReturnOfOverloads!fn mvd(alias fn, T...)(T args) {
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typeof(return) delegate() bestMatch;
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int bestScore;
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ov: foreach(overload; __traits(getOverloads, __traits(parent, fn), __traits(identifier, fn))) {
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Parameters!overload pargs;
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int score = 0;
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foreach(idx, parg; pargs) {
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alias t = typeof(parg);
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static if(is(t == interface) || is(t == class)) {
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pargs[idx] = cast(typeof(parg)) args[idx];
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if(args[idx] !is null && pargs[idx] is null)
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continue ov; // failed cast, forget it
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else
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score += BaseClassesTuple!t.length + 1;
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} else
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pargs[idx] = args[idx];
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}
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if(score == bestScore)
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throw new Exception("ambiguous overload selection with args"); // FIXME: show the things
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if(score > bestScore) {
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bestMatch = () {
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static if(is(typeof(return) == void))
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overload(pargs);
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else
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return overload(pargs);
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};
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bestScore = score;
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}
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}
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if(bestMatch is null)
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throw new Exception("no match existed");
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return bestMatch();
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}
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///
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unittest {
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class MyClass {}
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class DerivedClass : MyClass {}
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class OtherClass {}
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static struct Wrapper {
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static: // this is just a namespace cuz D doesn't allow overloading inside unittest
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int foo(Object a, Object b) { return 1; }
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int foo(MyClass a, Object b) { return 2; }
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int foo(DerivedClass a, MyClass b) { return 3; }
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}
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with(Wrapper) {
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assert(mvd!foo(new Object, new Object) == 1);
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assert(mvd!foo(new MyClass, new DerivedClass) == 2);
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assert(mvd!foo(new DerivedClass, new DerivedClass) == 3);
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assert(mvd!foo(new OtherClass, new OtherClass) == 1);
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assert(mvd!foo(new OtherClass, new MyClass) == 1);
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}
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}
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