How to implement call caching (Memoization) - dart

Question

I want to implement call cache(memoization) in non-intrusive way with the metadata annotations.
Hopefully, it will work like this:
class A{
#Cached
foo(msg) {
return msg;
}
}
void main() {
#Cached
var foo = ()=>"hello";
}
Can it be achieved with only dart:mirrors ?

Answer 1

I wrote a whole blog post on this topic a while ago. It's too long to copy here, so here's the link:
http://dartery.blogspot.com/2012/09/memoizing-functions-in-dart.html
The upshot is that you can write higher-order memoizing functions, but they're limited in generality by Dart's lack of flexible args functions. Also, if you want to use dynamic programming with recursive functions, you need to write your function with memoization in mind - it needs to take itself as an argument, so you can pass in the memoized version.

Answer 2

My current solution allows:
class B {
#CachedCallName(#cachedBaz)
baz() => print("first call to baz");
}
class A extends B with CacheableCalls {
#CachedCallName(#foo)
_foo(msg) {
print("first call with: $msg");
return msg + msg;
}
}
void main() {
A a = new A();
print(a.foo(21));
print(a.foo(21));
a.cachedBaz();
print(a.foo(22));
a.cachedBaz();
}
Output:
first call with: 21
42
42
first call to baz
first call with: 22
44
Flaws:
- can't cache methods with their actual names.
- can extend collection view but can't cache existing operators like operator []
- can't cache functions.
Full source:
#MirrorsUsed(metaTargets: CachedCallName)
import 'dart:mirrors';
class CachedCallName {
final Symbol name;
const CachedCallName(this.name);
}
#proxy
class CacheableCalls {
Map _cache = new Map();
dynamic _chacheInvoke(InstanceMirror thisMirror, Symbol
methodName, Invocation invocation) {
String key = "$methodName${invocation.positionalArguments}"
"${invocation.namedArguments}";
if (_cache.containsKey(key)) {
return _cache[key];
} else {
InstanceMirror resultMirror = thisMirror.invoke(methodName,
invocation.positionalArguments, invocation.namedArguments);
_cache[key] = resultMirror.reflectee;
return resultMirror.reflectee;
}
}
dynamic noSuchMethod(Invocation invocation) {
bool isFound = false;
var result;
Symbol called = invocation.memberName;
InstanceMirror instanceMirror = reflect(this);
ClassMirror classMirror = instanceMirror.type;
classMirror.instanceMembers.forEach((Symbol name, MethodMirror mm) {
mm.metadata.forEach((InstanceMirror im) {
if (im.reflectee is CachedCallName) {
if (im.reflectee.name == called) {
isFound = true;
result = _chacheInvoke(instanceMirror, name, invocation);
}
}
});
});
if (isFound) {
return result;
} else {
throw new NoSuchMethodError(this, called,
invocation.positionalArguments, invocation.namedArguments);
}
}
}
class B {
#CachedCallName(#cachedBaz)
baz() => print("first call to baz");
}
class A extends B with CacheableCalls {
#CachedCallName(#foo)
_foo(msg) {
print("first call with: $msg");
return msg + msg;
}
}
void main() {
A a = new A();
print(a.foo(21));
print(a.foo(21));
a.cachedBaz();
print(a.foo(22));
a.cachedBaz();
}