Geek asks and answers

How to implement dynamic properties in Dart?

I would like to be able to return a dynamic property using a map using a search in noSuchMethod (). However, recent changes make the link name of the inbound property unavailable. I can understand a minimization scenario that requires us to use characters rather than strings for names, but this makes it difficult to implement serializable dynamic properties. Does anyone have any good ideas on how to approach this problem?

  • I cannot use line names, since line names are not fixed between minifier calls. (This will completely disrupt serialization)
+5
source share
3 answers

You can access the original name with MirrorSystem.getName(symbol)

Thus, a dynamic class might look like this:

import 'dart:mirrors';

class A {
  final _properties = new Map<String, Object>();

  noSuchMethod(Invocation invocation) {
    if (invocation.isAccessor) {
      final realName = MirrorSystem.getName(invocation.memberName);
      if (invocation.isSetter) {
        // for setter realname looks like "prop=" so we remove the "="
        final name = realName.substring(0, realName.length - 1);
        _properties[name] = invocation.positionalArguments.first;
        return;
      } else {
        return _properties[realName];
      }
    }
    return super.noSuchMethod(invocation);
  }
}

main() {
  final a = new A();
  a.i = 151;
  print(a.i); // print 151
  a.someMethod(); // throws
}
+8

" ", . , . .

: ( , new Symbol) , , , .

0

You can do something like this:

import 'dart:json' as json;

main() {
    var t = new Thingy();
    print(t.bob());
    print(t.jim());
    print(json.stringify(t));
}

class Thingy {
    Thingy() {
        _map[const Symbol('bob')] = "blah";
        _map[const Symbol('jim')] = "oi";
    }

    final Map<Symbol, String> _map = new Map<Symbol, String>();

    noSuchMethod(Invocation invocation) {
        return _map[invocation.memberName];
    }

    toJson() => {
        'bob': _map[const Symbol('bob')],
        'jim': _map[const Symbol('jim')]};
}

Update is a dynamic example:

import 'dart:json' as json;

main() {
    var t = new Thingy();
    t.add('bob', 'blah');
    t.add('jim', 42);
    print(t.bob());
    print(t.jim());
    print(json.stringify(t));
}

class Thingy {
    final Map<Symbol, String> _keys = new Map<Symbol, String>();
    final Map<Symbol, dynamic> _values = new Map<Symbol, dynamic>();

    add(String key, dynamic value) {
        _keys[new Symbol(key)] = key;
        _values[new Symbol(key)] = value;
    }

    noSuchMethod(Invocation invocation) {
        return _values[invocation.memberName];
    }

    toJson() {
        var map = new Map<String, dynamic>();
        _keys.forEach((symbol, name) => map[name] = _values[symbol]);
        return map;
    }
}
0
source

More articles:


All Articles